That was very interesting snickerdoodlesmom. I didn't know chinchillas did that. I hope that hampsterblade's pet is the same kind of deal.
For now the best thing to do is just monitor and watch for changes. If she does go off her food then you know it's serious. If she stops eating you should still be able to go the vet and get the supplies, mainly critical care and a feeding syringe, to start feeding and keep her alive until you can make an appointment. The best case scenario is that it is a pulled muscle and it will get better in a few days. The second best case is that it is a behavioral issue. It may never go away but it is not dangerous. Another slight possibility is fur fungus such as ringworm but the pattern of the biting from what I can tell doesn't indicate that. Ideally she should be examined by a vet to make sure she is not in danger.
Unfortunately it's going to be hard to tell what it is because chinchillas in general do not like people to mess with their legs to examine them. Perhaps you can try again when it is not in the middle of fur biting. Also watch to see if there are any abnormalities in his walking or jumping. That could also be an indicator of injury. If everything seems normal there I wouldn't be extremely concerned.
If it's fur biting by itself then look for things that can stress her out. Chinchillas need about 12 hours of light per day and 12 hour of darkness and prefer to sleep during the day. She should never be put in direct sunlight, should be kept in a peaceful place, should not be exposed to music or electronic noises constantly, should be kept away from other pets such as dogs or cats that may taunt them, and should be considered extremely sensitive to noise and commotion. Some chinchillas are more prone to fur chewing than others.