Bunnies do often get hock sores when they live on a grid. For now, I'd bandage it and keep it as clean as possible until she can see a vet. When animals are hurt, they NEED to see a vet. Legally, it's animal cruelty to not take your pet to the vet when she is injured. She can easily get a bad infection without proper treatment, which will only rack up the vet bills much, much more and could lead to more serious illness. Please tell your Mom that.