Having the flora out of whack (such as yeast overgrowth) just ruins the normal viscosity of vaginal fluid, so it doesn't work and you can get little injuries such as you describe. Take a prebiotic, cut way back on sugar and simple carbohydrates (no soda or fruit drinks or pasta or white bread). Take odorless garlic, eat yogurt. If those don't turn it around, you can get an oral pill for yeast from the doctor. Diflucan. Don't try to have intercourse until it gets back to normal.
The ob/gyn can swab you for yeast and tell you if you have an overgrowth during an appointment. They go look under a microscope. Diflucan is my preferred treatment, but they also make creams and suppositories to use. Antibiotics often cause rebound yeast infections, because they kill off bacteria in the vagina, allowing the natural yeast to overgrow. And sex with a yeast infection can cause abrasions and a bit of bleeding.
Yes yeast infections can cause cuts as I have chronic yeast infections for over 20 yrs. Cutting out gluten and Dairy helped with that for the most part.
It is possible that it could be bacterial vaginosis did she do a swab for that again to see if it went away or not? If it is BV then you would need another antibiotic.
So to me it sounds like the skin is sensitive right now and because it is itchy its causing the cuts. Do you have over the counter dufflican? They sell it now in Canada but not sure anywhere else. It is what they used to give in the doctors office but because so many women have YI they decided to put it over the counter since things like monistat and canestan dont always work for some people, and I am one of them