Sounds like it might be interdigital pyoderma. Here is some information:
Skin issues are usually a symptom of an underlying problem - from a homeopathic view, an imbalance in the Vital Force. Until the Vital Force is brought back into balance, the symptoms will continue. If they are suppressed (i.e., 'treated'), they can internalize and become liver, kidney, digestive, etc. issues. It is important to discover the underlying problem before attempting to 'cure' the skin issue.
Consulting a holistic or homeopathic veterinarian is something to consider. You've tried the conventional route, and it obviously is not working for your girl. A h/h vet will look at the entire picture - diet, environment, history, vaccinations, other medical issues, etc. - and make treatment recommendations based on the entire dog, not just the one symptom. A diet change will probably be suggested, and is usually extremely effective in relieving skin issues.
Other things you can try are rinsing the paws with an apple cider vinegar (the unpastuerized, unfiltered kind) dilution (this stings, so make it very dilute if the sores are open/oozing), or giving acv in the food or water (some dogs don't like the taste, others do). Raw honey would probably help but she'd lick it right off
Colloidal silver may help, a few drops on the sores a couple of times a day. But again, these are only palliative remedies to relieve the symptoms; they do not address the underlying cause.