Chicken seems to have injured herself

This morning I noticed my young hen laying down, neck on the floor, legs poised over her head. Under her wing there seems to be a gash, as well as dried blood all over her feathers. As I was looking for vets (our normal one is on vacation) she sprang up and stood on her feet, albeit uneasily, for a long while. Now she is sitting on her hind legs, trying to tuck her head in her wing periodically. I have an appointment for this evening, nothing was available any earlier. Does anyone know what could have caused this, or what to do?

I'll note that she is still eating and drinking. There is no possibility of attack from dogs or others birds, as she has been isolated inside my home until she grows, and is put in a baby brica at night time, when this happened. She can still walk if she tries to.

Update: I applied a water/hydrogen peroxide solution and then topped it with neosporin cream on and around the wound. She didn't struggle much, but has now taken to 'flopping around' while she was sitting quietly before.

Welcome to BYC. Could a rooster have injured her with a spur while mating? She sounds like she is not doing well because of the flopping around. I'm not sure of what else you can do for her at this point except for giving her supportive care such as keeping her warm, offering her some electrolytes, and give her some eggs. Check her side for any puffiness that could be air under her skin from a leaking air sac. She may have internal injuries if she fly or fell into something. I hop she makes it to the vet. Let us know how it goes.