I checked her feet and they look good. I think it might be her hip or knee? She limps much worse after she's been laying down for a while, but while it is a little better with use, it's still very pronounced.
The best guess I can make is she pulled something while running from one of the big girls. They've been integrated with my 5 adult hens for about 3weeks. For the most part, everything is peaceful, but my head hen, a barred rock sometimes gets a burr up her butt and patactically stalks them. I have lots of little hidey holes for them, and I don't think that she actually got caught since there are no actual marks on her.
Sounds like a leg/hock strain to me. The limping more right after she stands up is why I say that. I have elderly hen with severe arthritis in one hock joint and after they've been laying down for awhile, they limp badly for a bit after they stand up. Legs can easily be injured in chicks running for their lives. Also, if the hock juts/bends out to the side oddly, it can be a slipped tendon. That is something I've never been able to fix on the rare occasion it showed up in a chick, but sounds like yours just pulled something. At least, that's my guess from the way it's presenting.