We have a stray cat, who has been in our home for over 3 years.
She's a calico and appears never to have been fixed.
She was wild outdoors through 3 winters here in Vermont.
Today, all of a sudden, she's bleeding or menstruating out her vagina.

OR, could she have a urinary track infection?

Did the vet shave her stomach and look for a scar that could have been from being spayed.If not, more than likey she is in heat.Some cats especially very small cats mature later in life,but it could be a UTI also.You can take her to the vet and have a check down on her urine to make sure.There is also a new item on the market that will check for bladder and urinary problems for women,and I think this product will work for a female cat also.I think it is made by vagisil,so you may want to give it a try.It is hard to tell if a cat has been spayed,so finding a scar is sometimes like finding a needle in a haystack.

By this morning she wasn't bleeding quite to profusely, and apparently it seemed to only be an UTI, but she was still uncomfortable, so we took her to the vets. I neglected to say that she appears to be 10 +/- years old. Anyway, it looks to the vet that it may be a thyroid problem w/UTI adding to it. We will know tomorrow. Thanks for your help.