Thank you to everyone again for your input and help calming this mama chick down!
We went to see the vet and she is one lucky chick!! We scared the coyote right in time before he could do true damage. She does have exposed muscle and fat tissues, but no organs were punctured or injured. She should make a full recovery in a couple weeks, yay!
The vet recommended:
meloxicam for pain,
continue oral amox/clav for 2 weeks and
silver sulfadiazine cream to apply as needed to her wound.
She will be in isolation until her skin grows back to prevent other chickens from pecking at her wound.
I feel so relieved and full of hope. Chickens are truly resilient little birds and I adore their fluffy little butts!