Hi there!
For the purposes of this I will be primarily focused on the 18th century, and it may wander into army wives as a broader topic, but I'll try to keep focused. In addition a lot of the sources I will cite are primary sources based on my own research (which deals with the experience of the British army in Ireland in the 18th century) so I'll put transcripts of material in as well as references as it may be difficult for you to chase them up.
Generally, a distinction needs to be drawn between the experience of officer's widows, and the widows of the rank and file. Most of the information available details the officer's widows, as can be expected with military history generally in this period. We're still working on that history from below! The wives of the rank and file are viewed more as an inconvenience than anything else. When regiments were told they were to be serving abroad, often officers would forbid their men from marrying because they knew married men were more likely to desert, or they would have to provision for the wife of the soldier.
"it is notorious that soldiers in most quarters can without difficulty find wives ; but in the north of Ireland, wherever the regiment was stationed, young appeared to have a predilection for our men, and it being expected that we should shortly be sent to serve in America, the commanding officer issued a general order to prevent them from marrying without a written permission, signed by the officers of the company or detachment." (Writings of Roger Lamb, p. 74)
There are some exceptions to this, such as regiments sent to Nova Scotia in 1749 who were actively encouraged to bring their wives and children (MS9616 n.2763, Lords Justices to Bedford, April 24th 1749). But generally a soldier's wife, and indeed widow, is hardly the most cared for part of the military administration! Screen alludes to the widows of rank and file receiving a small payment, but this pales in comparison to the officer's widows. (Screen, 'The Eighteenth Century Army at Home as Reflected in Local Records', JSAHR Vol 88 N.355, 2010, p. 230)
Considering the officers widows, the state did make an effort to take care of them. Most of the 'looking after' would be monetary. Here is a link to a photograph taken of the journal of the Irish House of Commons (Vol 19) in 1779 which shows £5569 has been spent on provisioning officer's widows within the Irish military establishment. Comparing that to some of the other expenses, it's telling that that amount is 1/3 of the amount spent on invalides. Given Ireland had one of the largest military hospitals in the Empire, this expense on wives is clearly not an afterthought. However, when we look at the total budget of that year, it is only 1.27% of total military spending. So while they did care, they didn't care that much!
In practice however, this sum was more of a token gesture than anything else. There are several cases of officer's widows protesting their current situation and demanding the state either pay the money they are owed, or increase the pay they are being offered.
" A petition of the officers widows on the Irish establishment, setting forth their deplorable condition, by reason of having five years arrears of their pensions due to them, and praying this house will take their distressed case into consideration, was presented to the house and read." (Journal of the house of Commons of Ireland Vol. 6, p. 94)
It also appears that the commission of the officer passed to the wife on certain occasions, and that in dire situations these commissions could be sold back to the army for financial recompense.
Whitehall, 9 March 1785
To Rutland
"I have laid before the King your Grace's Letter of the 25th ultimo, inclosing the petition of Ann Squire, widow of John Squire, Major/late captain in His Majesty's 61st Foot, praying leave that the Commission on second may be sold for the benefit of herself and four children according to the first resignation given in by the said major, and I have the satisfaction to acquaint your grace that His Majesty from your Grace's Particular recommendation as well as the distressed situation of the family is graciously pleased to consent to the disposal of the said commission enclosed." (HO/100/15, p.66)
Overall, the army did at least try to provide financial compensation for an army widow. However in practice, it seems that this was a token gesture, and not top on their list of priorities in the 18th century.
Let me know if there is any follow up questions I can answer, or if you want further sources on the subject.
edited formatting on quotes