What is the ruling concerning the fasting and prayer of a woman who believed that her menstrual blood was istihāḍah (non-menstrual vaginal bleeding), but then realized after Ramadan that it was in fact menstruation?

The days you fasted during menstruation must be made up, as well as the prayers you performed after the cessation of menstruation but before performing ghusl, because they were not valid. It is more cautious to make up those prayers, in agreement with the opinion of the majority of scholars.