I would avoid hydrogen peroxide and using antibiotic ointment on her.
Hydrogen peroxide is VERY harsh on a chicken's delicate skin... not to mention intestines. Use either betadine OR chlorhexidine (you can get it at Walgreens by the hydro perox or order it by the gallon online). It burns a little, so hold her tight.
If you use chlorhexidine, you will NOT need to use antibiotic ointment.
Flies and maggots LOVE dark, warm, goopy places. Filling her full of ointment MIGHT make matters worse, even though you're totally trying to help.
I hope she makes a full recovery!! Just watch her to see if she goes off her food and water. I'm glad she's still eating and drinking!
You're doing a great job.
MrsB