If there is one, take her to the vet. If there isn't one, the mouth opening thing might be unrelated to the attack. If she's acting normal other than the mouth opening, she likely is normal, except for the wounds you described.
Her lungs are at the top of her back. If you're not familiar with the location, do a search in google for chicken lungs, and then click Images to see pictures of the location of the lungs. Do you see any puncture wounds under the back feathers where the lungs are?
Is her crop full? That stretching of the neck and opening her mouth can be a normal thing for chickens. You say she's alert and will drink. Other than the mouth opening, is she acting normal?