One of the things you need to prepare for is if she refuses to eat. If you have a vet, ask them to sell you a feeding tube and feeding syringe to have on hand if she needs to be tube fed. I got a tube and syringe from my vet for $3 for the two items.
You can look for baby bird formula which is balanced in nutrients for birds to tube feed her or just to feed her as her beak heals. You will be surprised how quickly a chick can heal. I also mix yogurt and strained baby meat together for a high protein food for sick chickens. Or raw egg yolk and baby meat.
I've been thinking of a scenario where a chick could sustain that kind of beak injury. I picture a raw edge of hardware cloth with a slight gap against a wood surface. The chick sees something behind the ragged wire edge and sticks her beak into the gap, snags it on the raw edge and tears the beak as she tries to wrench herself free. You need to look for such a raw edge where you have your chicks and tape it up or secure it with a wood furring strip.
