I think the aspirin is a good idea. I would just give her the dose orally, vs in water, that way you can make sure she gets a whole dose. If the aspirin works, maybe she will end up moving around a bit. But if she doesn’t want to move I wouldnt make her right now. Just keep her quiet and warm and make sure she’s eating and drinking. Set your expectations that this may take time to heal. Or as rebrascora said it could be something else. Just keep her comfortable and observe. If she’s getting better on the leg as the week goes on it probably is a leg injury.