I experienced this same thing and it turned out to be scale rot.... change the substrate to newspaper, keep her a bit dry (you can mist daily or twice daily) but keep her substrate dry..... Mine had to be on newspaper for two weeks, until he shed again, and then i was able to put him back on the coconut fibers... Don't mess around with this, it could get bad.......
Also you can start cleaning her belly with a nolvasan mixture... 1 part nolvasan 3 parts water.... clean her belly twice a day for a week or so, she should get better and shed out again soon.
I've learned that snakes with scale issues tend to shed more frequently.... so be prepared for her to shed again once the belly inflamation goes down.
Good luck
Teri