I would recommend reading this book about Cecilia Penifader of Brigstock. We know that she never married. She did own her own property, but also lived with the support of her brothers. She also had a large inheritance from her parents, who both died during the Great Famine in the first half of the 14th century.

English society was still male-centric, however, so Cecilia's brothers often had to act in legal and official capacities on her behalf. This is just one person, but does provide a good portrait of how a medieval woman would have acted if she wasn't married.

Much of Chaucer's Wife of Bath's Prologue discusses a late medieval woman's marital situation. Alison is a five-time widow who uses her sexual charms to get men to marry her, both for sex and for their property. To her fourth husband, whom she married when she was 40 and he 20 (her first marriage was at 12 btw), she gives the land and money that she had inherited from her previous husbands:

I shal seye sooth, tho housbondes that I hadde, / As thre of hem were goode, and two were badde. / The thre men were goode, and riche, and olde; (195-97)

Former husbands who she gets "wholly in hand" gave her all their lands. She's a gold digger who finds old, rich men, then seduces them to gain their wealth when they die:

But sith I hadde hem hoolly in myn hond, / And sith they hadde me yeven all hir lond, / What sholde I taken heede hem for to plese, / But it were for my profit and myn ese? (211-14)

She notes, too, that even if you were crazy ("wood"), she wouldn't let you have her body and her goods ("good"):

"Thou shalt nat bothe, thogh that thou were wood, / Be maister of my body and of my good" (313-14).

In an exception, she married her fourth husband (an Oxford student) for love instead of money:

"My fifthe housbonde, God his soule blesse, / Which that I took for love and no richesse, / He somtyme was a clerk of Oxenford" (516-17).

Unwisely, she give him all her holdings, which she soon comes to regret:

"What sholde I seye, but at the monthes ende / This joly clerk Jankyn, that was so hende, / Hath wedded me with greet solempnytee, / And to hym yaf I al the lond and fee / That evere was me yeven therbifoore; / But afterward repented me ful soore" (617-22).

IIRC, there are editorial footnotes in the Riverside Chaucer discussing the legal and economic situation at more length (which I would look up were my books not in boxes).

All this is, of course, anecdotal literary evidence, but Chaucer drew from life and was attentive to details like these, so it gives us something of an impression of one mode for women who were savvy enough to achieve a tenuous independence.

Source for quotes: http://www.canterburytales.org/canterbury_tales.html

Before the Black Plague and even until the 16th Century in some cases, brewing and selling beer was one of the main -- and comparatively lucrative and stable -- occupations that medieval (married and non-married) women could engage in.

Prior to this trade being increasingly commercialized and regulated over time by the 16th Century, women could work either alone or in tandem with their partners, on what appears to be remarkably equal terms.

Wikipedia has a surprisingly detailed and well-sourced entry on the matter. If a wikipedia entry isn't sufficient, then it extensively quotes the following source:

Judith M. Bennett, Ale, Beer and Brewsters in England: Women's Work in a Changing World, 1300-1600 (New York: Oxford University Press, 1996)

Women had it pretty tough, especially poor widows and unmarried women. I am sorry that I do not have many of my sources with me at the moment but I'll do the best I can to support what I say. Firstly my reading of gender in this period would be one of a very clear and powerful patriarchy dominating the social structures of the time. Women were held by many as the far weaker sex. Thomas Aquinas wrote “...the female is a misbegotten male… [and] …women [are] naturally of less strength and dignity than men… (I've taken that quote from L. Di Caprio, and M. E. Weisner (eds) Lives and voices: sources in European women’s history). I would argue that this attitude was still in force well into the Early Modern period. Most of the research I have done focussed on women and their idetiity through their work and I would call upon Women in Early Modern England, by Sara Mendelson and Patricia Crawford who stated "... all women ... were affected by the expectation that they would bear children". From here we can move on to understanding how widows and single women were treated.

Single women I know only a little but I think the understanding of women being both weaker than men and whose existence was defined by their singular, (socially enforced!) goal to have children, they were not given much in the way of opportunity to develop an economic identity. Taking just two examples, agriculture and domestic service, single women partaking in such work were often underpaid. See Bardsley, S. ‘Women's work reconsidered: gender and wage differentiation in late medieval England’ for some numerical evidence and the argument she presents in interpreting that data, is quite interesting and I feel her interpretation has merit. Given that women's work was underpaid it can be assumed that eking out an independent existence would be next to impossible. Saying that there is evidence (that I cannot find right now!!) that single women working as domestic servants on an economically large estate/manor/household, probably could make a decent living given that she was often fed and sheltered as part of an arrangement with her master. Though I cannot recall any women working in such an environment and becoming independently wealthy (relative to other similarly classed single women).

On widows, they would have far greater scope for maintaining family wealth. Depending upon her husband's status; and this is key here, as a women was often defined through her husband. A widow whose husband was a guild member may well find herself able to continue running the family business, especially if she had some skills or journeymen working for her master (of his trade) husband. Some guilds would even help support a widowed family. Also a widow in England would be entitled to some of her husbands estate, and although a women running a business may well be frowned upon, it was shown that some widows survived and even thrived as head of a household business. Finally on widows (and there is much more but I would have to go back over my books to go into more detail) the evidence does point towards widows, especially young or wealthy (due to a late husbands estate) widows, looking to find a new husband quite quickly. Poor widows with children were perhaps some of the most destitute groups of people in this time period. Widows of agricultural labourers and other low skilled jobs would have little to money to support themselves following their husbands death and little chance of finding employment necessary for supporting herself along with any children. I'll again leave it up to Sara Mendelson and Patricia Crawford to summarise: "Isolation, loneliness, poverty, and increasing dependence [was] the lot of many widows...independence and autonomy ...enjoyed by only a few"

*NB research done for an undergraduate unit not anything spectacular!

Lyndal Roper wrote some amazing books on witchcraft and it all ties into the fact that unmarried women were targeted as witches. They were the midwives, cow milkers, child minders etc. So if the milk spoiled, a child died or got sick then it was that unmarried woman's fault. From the trials of these poor women we can get a good idea of what a unmarried or widowed woman of common birth would have done for a living. She would also have been very dependant on children or nephews for food and shelter. One of the Books was called Oedipus and the Devil.

Of all of the texts I would suggest reading, the one that gives the best idea of the lives of the urban poor would be Piers Plowman. The C-text or third version of the poem includes a lengthy section in chapter 9 (the chapters are called passus in the work, so passus ix) on the life of poor women. The text is written in a very difficult dialect of Middle English written in alliterative verse (where stressed words start with the same initial letter). Most translations are not of the C-text, so it's sort of hard to access passus ix without stumbling through the original language (which also includes two additional letters that are no longer part of English). Here's what the original text reads from manuscript HM 143 from the Huntington Library in San Marino, California:

Ac þat most neden / aren oure neyhebores
And we nyme gode hede / as prisones in puttes
And pore folk in cotes / charged with children
And chief lordes rente / þat they with spynnyng may spare
spenen hit on hous huyre / bothe in mylke and in mele
To make with papelotes / to a glotye with here gurgles
That greden aftur fode / and hem sulus also
soffre muche hungur and wo / in wynter tymes
And wakynge on nyhtes to rise to þe reule to rokke þe cradel
Bothe to carde and to kembe / to cloute and to wasche
And to rybbe & to rele / rusches to pylie
That reuthe is to rede / or in ryme shewe
The wo of this wommen / þat wonyeth in cotes
And of monye oþer men þat moche wo soffren
Bothe a fyngred and afurste / to turne þe fayre outward
And ben a basched for to begge / and wollen nat be aknowe
what hym nedede at here neyhebores / at noon and at eue
This he woet witturly as þe world techeth
What other byhoueth / þat hath many children
And hath no catel but his craft / to clothe hym and to fede
And fele to fonge þerto / and fewe panes taketh
There is payne and peny ale / as for a pytaunce y take
And colde flesche and fische / as venisoun were bake
Fridays and fastyngdays / a ferthingworth of moskeles
Were a feste with suche folk / or so fele cockes

¶ These are Almusse to helpe / þat han suche charges
And to conforte suche coterelles / and crokede men and blynde
Ac beggares with bagges þe whiche brewhous ben here churches
But they be blynde or to broke / or elles be syke
Thouh he falle for defaute / þat fayteth for his lyflode
reche ȝe neuere ȝe riche