You really need to somehow get that snake to an exotic vet. The vet saying a culture would be useless is a useless vet. A culture will tell you exactly what you have and what antibiotics will work the best. As of right now, she is just throwing medicine at the snake hoping something works and antibiotics are already harsh on a reptiles system especially Baytril. I had to give Baytril to my beardie for an RI and along with that, I had to give her a slurry dinner fortified with probiotics through a syringe. Baytril kills everything including good bacteria in the gut. The stuff works good when the bacteria is susceptible to it, otherwise you are doing more harm than good.

Tell the vet you want a culture done so she can pinpoint what exactly the bacteria or virus is so she can prescribe the right medicine the first go around. Or like I said, expand the search. My vet is over an hour drive away but well worth it imo and I live in an area with lots of vets who are way closer, some as close as 10 mins away.