@cow whisperer
It's very important to remove all the maggots.
Using Peroxide was fine for this first cleaning, but from this point forward use saline or soapy water (you can use Dial Soap or Original Dawn dish liquid) to wash/flush the wound to rid it of any more maggots.
Dry your baby well - if you need to, use a hair dryer set on low to dry her. Apply some triple antibiotic ointment or Vetericyn to the wound.
Watch the wound to see if any more maggots appear.
If the hen has more chicks - it would be a very good idea to move her and the chicks to a clean, safe environment. Inspect the hen and all the chicks for signs of maggots and treat according.
FWIW- Anytime you find maggots on an animal, they should be removed and the wound should be thoroughly cleaned, monitored and cared for. Maggots are used in the medical field, but these are "medical maggots" that are raised in a sterile environment and are bred to feed only on dead tissue, they are also carefully applied and monitored by a medical professional under controlled conditions. These are completely different than what you would find in an animal wound.