It can occur during a UTI, and it can be complicated by the fact that the bleeding went on for SO long without being untreated as the infection raged. She may have permanent damage to her urinary tract at this point.
Typically, bleeding from the vents occurs with urinary tract infections, certain types of cancer, and kidney/bladder stones. I would recommend getting an x-ray to rule out cancer and stones, just given the enormously long time this has occurred. I'm really surprised she's even alive after bleeding for 6 months.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry