Mud fever can be a pain to deal with. If its super bad the vet may need to give you something a bit stronger. Here is a site with more info Mud fever - Wikipedia, the free encyclopedia
for other treatments. Are you keeping her away from the area that she got the mud fever. Try some human antibiotic. The topical kind. My horse has a bad infection on his sheath once. I started to put neo-sporne on it, boy it cleared it up fast.