If she has her appetite, is happy and alert, and her poop is normal, then it could well simply be a physical injury caused by a rooster mounting her heavily, jumping and landing awkwardly or something similar.
If she is happy to take her weight on one leg then you could look in to rigging up a 'chicken sling' for her (a search on google will give you loads of pictures and ideas). This would let her be in a better position during the day (I would be inclined to let her lay down at night to roost as usual though), and to start to put a bit of weight on her bad leg if she feels able.
A leg injury can take quite a while to heal - I had a bird that jumped and landed awkwardly, and she limped for at least a month, although I very (very) gradually saw improvements.
Let us know how your bird gets on - she is lucky to have someone like you who cares so much for her.