Leg Injury Most Likely Caused by Other Hen

[Otterpop]

So this is my second chicken incident in less than a month. The last chicken (a Rhode Island Red) got pecked on by my bigger and bossier Barred Rocks. This morning I just noticed that the other Rhode Island Red is having some issues with her leg. She's limping and holding it funny and can't seem to make it up the ladder into the coop.

The two breeds are only three weeks apart, but the Barred Rocks are significantly bigger (and did I mention bossier?!) The Rhode Island Reds are much more sociable but don't seem to be able to stand up to the two bigger girls. What can I do about this?!