My horse had to have a large sarcoid removed from his groin on the inside of his hq. After cryo treatment there was a massive open wound similar to your mares. The whole area took about 10 months start to finish to completely close up and heal. I used an antibiotic scrub, betadine and water almost every day to keep it clean. Wear gloves (that stuff stains) and use clean gauze each time.
Keep a good lookout for any proud flesh formation and nip it in the butt really quickly- if any does form I'd recommend Proudsoff. It has worked better than any other remedies I have tried.
Vetricin is another spray that seemed to help with the healing process. I think originally wrapping it is good, but when you change the bandaging give it a few hours to breathe.
It will be a slow heal, just keep a close eye on it.