That sounds really tough. I'm sorry you guys are having to go through that.

Psychotherapy is very important as there are clearly some mistaken beliefs and faulty thought patterns that are leading your girlfriend to continue with this dysfunctional cycle of anxious behavior. Getting good psychotherapy isn't always easy though. Strangely it's not as easy as just turning up at a professional's office, as many don't click with their therapist. It can take multiple attempts to find somebody who understands what's happening in your mind.

If you still want to go down the med route, there are other categories other than SSRIs. Usually, doctors advise trying one more SSRI after the first one doesn't work (maybe something like citalopram, as it's "one of the more relaxing" SSRIs), then trying a different class, like maybe an SNRI.

From experience I can say that when you find the right drug, it makes a big difference, and very quickly too. All of a sudden you go from being completely on edge and impossible to deal with, to fairly relaxed and more like yourself again. They can reduce anxiety by up to 70% in some cases, which is just a colossal difference.

Keep hanging in there. Most anxiety disorders do get better when they're tackled head on.