My 4 week old kitten is dragging her back legs?

My kitten has been dragging her back legs but I haven't seen anything happen that might've hurt her, shes an outdoor kitten so I'm not always with her. We have no chance of taking her to a vet so is there anything I can do at home or can it heal on it's own. I love her and don't want to let her go... So to sum this up what possibilities can this kitten have and how can I help without taking to the vet.