Need help now! My kitten ate her litter!?

So my kitten is ate her litter(i don't know why) and now she is acting really strange. She won't play with her toys, she barley moves, she has indents on her belly, she is limping, and she falls if you try to pet her. I'm really scared and my sister called to the vet he doesn't know what could happen to her and my mom thinks she won't last the night. I need help PLEASE!