Hi Goldie - welcome! I'm sorry to hear about your fistula situation - my heart goes out to you.
I am much in the same position as you are. Had my pouch about 18 years when I developed an abscess just outside the v. which led to the discovery of a pouch-vaginal fistula. The v. side of the fistula is just outside of the v. opening.
I went to Cleveland (Dr. Hull) who told me this fistula would not heal (she 100% guaranteed it), so she put in a seton about 2 months, ago, and told me my options were 1) pouch redo (not interested); 2) pouch removal (maybe, but not now); and 3) leave the seton in for 3-4 years, take it out, and see what happens, which I'm not happy about, but is the course I'm currently on. Crohn's is a possibility, but it really doesn't appear that I have it, and a pouch redo wouldn't be possible with Crohn's. The seton does, at this time, keep me from marital relations as well, although Hull said I can go ahead with it - ha! Easy for her to say! She did stress that i/c won't harm the fistula/seton.
She told me the flap repair had a 10% chance of working (at least on my fistula)and that she rarely does them anymore. The plug she said has a closer to 0% chance of success. She seemed to favor the pouch redo (advancement, in your case?) All that being said, there are women on here who have tried the flap, the LIFT, gracilis flap, mesh (GinLyn), and other procedures, and have had mixed success. You can click on the "Find" button on the top of the page, and search for these various terms for some great information on these procedures.
I understand your nervousness about choosing an option - fistulas are very tricky and are not easy to get rid of. In my case, having the seton in gives me some peace of mind that the fistula has less chance of branching, abscessing, and causing other problems while I try to do research and consider the options.
This may not give you any guidance, but I wanted to let you know that you have quite a bit of company here, and that hopefully some of the others who have had the procedures can let you know more about their success.
Feel free to PM me if you'd like -