Sorry about your girlie there, looks to me like she may have been attacked. What else is in the tank with the frogs?
Did it just look like this all of the sudden, or did it start smaller and progressively get worse?
Compare her legs to the legs of any other ADF
's you have...are they much redder?
I would isolate the frog and keep the water absolutely prestine. Dose with 1 TBSP salt per 5 gals. Make sure you are always letting salt completely disolve in the water before adding it to the tank. Feed only thawed frozen foods..no pellets, and remove anything uneaten within an hour.
To clarify, are you saying you called vets asking about antibiotics for amphibians and they said they had nothing to offer?