I am not experienced in beak injuries, but that one is pretty bad. My guess is that she was attacked by a predator, but they can also tear up their beaks on wire fencing. Was she in a predator proof run when this happened? Was anyone looking in on your chickens? What all do you have in the flock with her? She may need to be tube fed fluids and food since she may not be able to eat normally. Can you try getting her to drink some fluids with electrolytes, and maybe give some watery chicken feed made very runny, and some soft scrambled egg? You can try to clean up her beak and mouth later, but she may need fluids right away. Vets can set you up with a syringe and feeding tubes, and you can buy some online. KayTee Exact bird feed can be fed through a tube, and you can find it at pet stores, Walmart and online. Here is a video of a vet tube feeding a chicken: