This question makes two assumptions. First, that women didn't work in medieval Western Europe. Second, that workers got paid.

In general, I don't think either assumption represents common medieval experience—at least for the early Middle Ages, which is my wheelhouse. Women did all sorts of important work and if you were wealthy enough to buy a slave, it was most likely going to be a woman. Of course, medieval slavery like most forms of slavery was often sexually abusive, so some of this work was sex work, predominantly as concubines although in some cases seemly as enslaved prostitutes. For example, the Law of the Northumbrian Priests regulated priests' concubines in northern England around 1020, and Charlemagne famously had a handful of known concubines in addition to his several wives in the years around 800.

Whether slave, domestic servant, or wife, women's work around the house was vital. They raised children and served as nurses and wet-nurses. They prepared pots for cooking and keeping food, ground grain, brewed beer, cooked meals. These seem to have been common roles, although women were often seen as being in charge of all domestic life. For example, women of Viking-Age Norway were often buried with sickles for reaping grain, and women across Scandinavia were often buried with keys that seem to have represented control over household necessities and wealth.

Women's domestic work could also become to producing sellable household surplus. They sheared sheep, spun yarn, wove cloth, made clothing. This made them the most likely producers of cloths and clothes that were traded, as well as the sails that moved people and goods across the medieval world. Textile production gradually became male-dominated work in the later Middle Ages, but the Bayeux Tapestry remains one of the best known medieval artifacts and almost certainly one made by women's hands. Charlemagne seems to have had whole factories of women making textiles in gynaecea, and some of his surviving diplomatic correspondence deals specifically with the textile trade.

Elite women also engaged in cultural and intellectual production. In England in particular, women had a long history of running not just nunneries but also the uniquely English institutions of joint nunnery-monastery. In Germany, the best known example is Hildegard of Bingen, who is known for her expertise in botany, medicine, and music, as well as for her mystical visions. In 1970, she was elevated to be considered a Doctor of the Church in recognition of these contributions. Other medieval women recognized as Doctors of the Church are more commonly celebrated for their role as mystics, which was a potentially powerful role during the Middle Ages.

So far, none of these women would have been paid—even though they certainly did work that was alternately politically, economically, socially, and culturally significant and highly valued. Again, female slaves were prized captives and prized purchases through much of the Middle Ages. But if women weren't paid, men doing corresponding work weren't paid either.

Male farmworkers during the early Middle Ages were paid only by the fruits of their labors, some of which they typically had to render to their lords or masters. Male household heads might have benefited the most from this production, and they might have even been the ones to carry things like cheese and textiles to the market, but the things they bought and maybe even the money itself would often have been managed by women once they returned home. Secular males of all occupations often had to render military service, and this was typically rewarded with prestige, gifts, or booty, but no payment per se. Ecclesiastical males like monks often did work more closely related to their female counterparts and likewise received no pay, although wealthy benefactors and surrounding communities might contribute to the church, monastery, or nunnery that housed them.

Things started to look different in the later Middle Ages, when economic systems and ideas about gender start to look more recognizable from a modern standpoint. But for the early Middle Ages, at least, it's possible to see women doing all sorts of work albeit in an economy where labor wasn't typically exchanged for cash payment.

Edit: Trimmed things up a bit to focus more tightly on the early Middle Ages in particular.