I’ve seen blood in one intercourse after 10 months of menopause. Must I go to the mikve?
In general any woman that sees blood has to go to through the tahara process, i.e. checking herself at the end of the fifth day, 7 clean days, mikvah etc. even if she is after menopause. (We can look at it positively, that you now have one more chance to fulfill this mitzvah, that you thought was already totally lost!) If you have reason to believe that you have some sort of wound, scratch etc. then the halacha might be different, if that is the case let me know.
(As a side point, a woman that bleeds after menopause should have it checked out by a doctor, just to make sure everything is alright).