So sorry to hear about your daughter's situation. Poor thing (and you!)
I've had a pouch-vaginal fistula for 3+ years now. It originates at the dentate line, and exits just outside the vag. opening.
It became known when it abscessed, although I was quite sick for years before that (fevers, headaches, flu-like). I do not recall anal pain with my fistula. I do recall air passing through, however.
The fistulas did not show up on a CT scan, however, they did show up on MRI which was only done due to the horrendous pain and swelling from the abscess. I did not have any of those other tests.
Cleveland Clinic (Shen) treated it with antibiotics and doxycycline shots, all to no avail, so he sent me to CR surgeon there.
She did a EUA and was able to locate the fistula's origination and insert a seton, which has been there for 2+ years now. Her recommendation was to redo the pouch, or go to end ileo, but she also said there was still no guarantee that the fistula would be gone with either option.
So, I'm one of those who has chosen to live with the seton for the time being, perhaps forever - I have not experienced infections and very little pain due to the fistula. 2 years later,there is typically very little discharge; discharge and air increases if I "hold" my BMs too long or eat seriously gaseous foods. I consider myself "fortunate" for having a relatively behaved fistula
I do toy with the idea of going to an end ileo, but my jpouch is functioning quite acceptably right now.
The seton creates no problems EXCEPT for making marital relations difficult/impossible, due to the seton's location. This, of course, is a biggie, particularly for younger women. I was told, however, that relations will not harm the fistula.
I hope you and your daughter find answers soon.