She needs to see a professional imo if you want any chance of saving her at this point I think. The substance is likely infection/puss, god only really knows if you don't take her to someone. The leg doesn't look good even to my untrained eye. From what I know of mammals when a limb swells regardless of reason, you reduce/cut off blood flow/supply which will cause the muscle and tissue to die. In essence kind of like a turniquet with out the external binding. If it is an internal infection the soaks aren't going to getthe job done. At this point internal as well as possibly external antibiotics might be called for.

Sending good vibes tho...