Well if she is really active she could have sprained her leg. If she wants to rest I would encourage it. Put food and water near her so she doesn't have to move.
Of course if she won't and would be more stressed forcing her to rest then I would let her be.
Just keep any eye on her good leg it...
You need to take a very close look from toe to as far up as possible to see if any wounds or deviations from the straightness of the limb.
Without pics or video it would be impossible to speculate. My young rooster tore a toe nail off and was limping around.
Look, feel, compare to the other...