well she really should see a Vet for xrays to determine if the hip is broken, if this heals wrong she may never get the use of the leg back
but it could also be just badly bruised, perhaps some ligament damage(?) without an xray its hard for me to advise you.
if its only muscle injury, it will heal itself. but if its broken than she will have lasting damage.
Watch her for another day and see if she attempts to at least try and use the leg, can she move it at all and just not putting weight on or what??
heres some info on fractures for you to read over, please keep us updated on her condition -)
I recommend a trip to the vet. Soon. There may be inflammation that is preventing use of the leg, so a steroid shot to reduce inflammation may help. At minimum, you would want a shot for pain as she is surely in some pain. Please consider taking the cat to the vet.