Sounds like your hen may just have a sprain or a pulled muscle. Provided there is no internal injury, with restricted movement, the leg should heal in less that a month. However, if there has been some sort of internal injury (I.E. broken bone, torn muscle/ligament, etc.) then the leg may not heal on it's own, or if it does, the leg may not heal correctly.
Does she put weight on the leg? Can she move all parts of it? Does she have feeling in her toes? Good blood flow? If so, then it is probably not broken. Typically a bird can receive this sort of injury from landing wrong off a perch, being jumped on by another bird, or just moving it the wrong way while running.
Should the leg get worse, there may be an injury that is not visible, or it may not be an injury at all, but rather a nerve or deficiency issue. Just make sure the bird has access to a good adult layer feed and you can supplement with lots of green veggies and fruits of all kinds. Be sure to monitor the leg and watch that it does not get worse.