I had my first hen with maggots this spring.....she had a poopy butt, apparently the flies got underneath, laid eggs, maggots wormed their way into her body in a big wound below the vent. I used an epsom salt solution (some epsom salts dissolved in warm water to flush the wound well. Then I sat with tweezers and picked out every one that I could find. Don't be afraid to work the wound a bit. I would squeeze it side to side and up and down to try and find all of the "pockets" of maggots. I had to do this 3 times before I came back to the wound and could not find any more (so 1 cleaning on day 1, 1 cleaning on day 2 AM and 1 cleaning day 2 PM). I believe I put some triple antiotic ointment on the wound, and kept the chicken in a brooder with wound exposed....not wrapped. I think that would be better than keeping it closed up, as long as there are no other chickens with her to peck it
If she is struggling, cover her head with a sheet, towel, etc. Make sure you don't smother the poor thing of course, but that will help her calm down. You really need to just get her covered up, flush the wounds well and pick all the maggots out with tweezers. Would be nice to have two sets of hands, one to hold the bird, one to do the flushing and picking.
My girl's wound was NASTY. It was pretty deep as well. But she healed up just fine and dandy. Within a month you couldnt even tell where the wound was.