What you describe seems like an abscess. The hair should be trimmed around the wound so it can stay cleaner. I hope your veterinarian or another can help you with that. Your cat might need to wear a cone if she continually traumatizes the wound. DERMA-IONX is helpful for many skin conditions. It is an oral homeopathic product which stimulates the enzyme systems in the body that aids the skin and helps with assimilation of nutritional components in diet and supplements. What sets it apart from most homeopathics is that it is in an oligotherapeutic mineral base which has had a charge added to it.
Initially I would give a half dose of DERMA-IONX on the breakfast and supper food. After there are signs of improvement you can give a whole dose once a day.
I would also give Probiotics to aid the immune system. OMEGA 3,6,9 is also helpful in soothing skin and improves coat quality.
Diet can also influence the skin. What do you feed your cat?
Please keep us updated so we can help guide you along the way.