You need to take her to a vet to diagnose what the problem is. If it is dislocated it can be popped back in, but a fracture may require different treatment. http://www.poultrydvm.com/condition/fracture
The link tells you how to immobilize and wrap the joint. You will need to give her some aspirin for pain http://www.poultrydvm.com/drugs/aspirin
The vet should prescribe some pain killer such as Meloxicam.
Good luck with her and keep us posted
Since it is a chick you may want to search this site for splayed legs. the easiest treatment I have seen is a cut off bit of a drinking straw and a rubber band knotted in the middle until you get the legs into proper orientation. Please research that condition to see if it sounds like your chicks issue.