NO peroxide, it can actually inhibit healing, and doesn't do anything for cleaning. I would do either chlorhexidine soaks or betadine, and using some gauze, scrub(lightly of course) the belly scales so the dead ones come off(debriding).

The Baytril is fine as I'm sure she needs it. I would just keep her warm and dry(normal humidity, but dry substrate).

I just can't see how her poor belly got that way in 3 weeks...