I am sorry to hear about your girl's problems.
My biggest question is that with your first veterinarian, when surgery was performed, was the mass submitted for pathology?
That is really where I believe the answer needs to come from to get an answer. Are these cysts (which would be my suspicion), or are the tumors of some type? A biopsy will give those answers.
If that hasn't been done, I would have it done soon, and ask your vet to make sure the samples are submitted to veterinary dermatohistopathologist. It's a big, fancy word, but it means someone who specializes in skin lesions.
When she was on systemic antibiotics, which ones were they? And how long and how frequently were they given? You might be surprised how often doses are given too low or too infrequently or even too short of a period of time to be effective.
I hope this helps!
As always, if you have further questions or concerns, please don't hesitate to ask them using the "reply" function.