Putting her in a wire dog crate, inside the coop or run or yard where the others live, can help her be less lonely, and can help the other chickens start to accept her as part of the group.
Or you could try putting just one of the other chickens into her coop, to keep her company. Of course supervise to see how it goes, but just one could be different than having them all ganging up on her. If you know which one is at the bottom of the pecking order, that's the one to try putting in with her.
If you are able to add one chicken, then after a while you might try adding another. You might even be able to gradually work back to having a single flock, just by adding them one-by-one to the group with the hen that was injured. The difference is that instead of her being a single newcomer, each other chicken would come as a newcomer to her group. This could take weeks or months, adding one at a time and then waiting a while, so it might not be worth the effort.