Oh, this is a toughie. As "mom" to a number of problem fur-children over the decades, the repetitive cat pee is the worst! Sounds like you've done all the right things, as far as medical and behavioral.
A few suggestions:
1. up the number of litterboxes you have in the house. Gross, I know, but if it's territorial peeing that might help. (I had a kitten once who, at four months, started peeing on the couch. My husband and I agreed that if he didn't stop by six months he was going to the pound. Then I remembered that we only had one litterbox for two cats, and that at his birth-mama's home they had an extra litterbox next to the sofa! I put another kitty potty next to our sofa and sure enough, the kitten jumped right in and started digging like crazy. Except for one lone incident, the peeing on the couch ended. We were also eventually able to move the box away from the couch, so it all worked out fine.)
2. we had a cat growing up who was the sweetest kitty ever, only he could not stop spraying. My mom tried everything from Valium to surgery but nothing worked. Finally she just turned him from an indoor cat who occasionally went outside to an almost full-time outdoor cat. Not something I'd reccommend for city folk, but if you live somewhere safe maybe you could keep her outdoors.
3. I had a feral cat for ten years. He was awful and peed on everything. Near the end of his life, the vet prescribed an anti-anxiety drug which worked for a little while.
Otherwise, good luck and keep us posted.