Another hen would be best for her, but I think I've read of someone keeping chickens and rabbits together here on BYC? Can't be sure though, maybe someone will chime in who knows the answer for sure.
Edited because I remembered a news story from about a year ago, I think it was in Australia (in a zoo maybe?), about the broody hen who took a litter of bunnies for herself? She kept them in her nest box and sat on them and tended to them. The mama bunny seemed fine with it and would come around only to feed her babies then she'd go on her way (I think that's normal behavior for mama bunnies). Don't know how it turned out but it was a cute story with video. I think the bunnies and chickens had always shared the same coop. You can google it, I'm sure it's on YouTube somewhere.