Thanks everyone. She's had tons of blood work done so I would assume testing for bacteria would've been in there too. I did even ask my vet once if she should be on a course of antibiotics for this (read that online) and she that yes, that could be one option. She never did do the antibiotics until she pooped blood and then she went on some but that was for the diagnosis of colitis.
This Wednesday I have an appointment at another new vet. I've been referred to them by about six different people now. The guy I'm seeing is young (which I like since he knows modern treatments well) and endoscopy is one of his specialties. My normal vet quoted me $3000+ for the endoscopy! This vet quoted 600-1200 and that's including blood work and a possible biopsy that they'd take from her tummy.
I'm terrified for her to have to go under anesthesia, especially because she's so stressed and scared all the time. But I've found most vets are good if I tell them and they've let me stay in the room while they put her under, or at least give her a relaxing drug. So I'm hoping for the best. Mostly I'm hoping for some answers finally!