If it's mainly the skin ripped off, she should be able to heal. Chances if the muscle is not ripped badly, it will have bled and helped clean out the wound lessening the chance of infection.
The two biggest things is keeping other chickens from picking on her, in which you've already mentioned you're isolating her AND keeping the flies off the wound. To me flies would be the biggest worry. I would keep her any place where she won't be exposed to any flies. I just had a hatching chick picked at and I used a new to me item which is a tube of disinfectant cream, which appeared to work really well. I have the chick in the house. Normally I'd use a diluted hydrogen peroxide spritz to spray the wound after irrigating the wound with lukewarm water to clean it up.
My horse once ripped the skin off it's front chest, and it healed perfectly using the diluted peroxide in a spray bottle. No infections or scar left.
For our large animals I do have a disinfectant/insecticide spray, but I'm not sure there's anything like that anymore. I bought out the store's stock when we heard it was discontinued.
When the hen is healed, she'll have bare skin exposed. Blu cote is very affective in covering up and preventing picking by other chickens.
It's what I just started using and it seems to work really well.
