I'm so sorry your baby was hurt. My baby Speckles is about the same age (born 7/8/05). He's also small for his age. Speckles was raised by his mother in the same pen as my other two hens and rooster but I put up a partition. You say you can't have another cage but can you divide that cage up?
Exactly what are the dimensions of your chicken house and run?
How old are those chickens (adult or young is fine)?
Can you divide the run up by throwing up some temporary chicken wire?
Can you buy/get a metal dog crate/kennel and put her in that within the main pen/cage/run? I've done both methods of separation where the chickens can't get to eat other but can see and interact with one another, hopefully getting used to each other.
Reading my experiences with Speckles at
http://www.fishpondinfo.com/chicken2.htm may provide some ideas or at least know that you're not alone. Speckles is harassed a little bit but is okay. It's interesting that in both our cases, the rooster (daddy) was amazingly nice. Chickens of both sexes can be quite barbaric and will kill each other. Before letting the chickens together, your baby has to heal. That can be done in a new subcage if you set one up (dividing up your run I mean). To treat the injuries over the counter, just rub some Neosporin in the wounds once a day. If she tries to eat it, iodine may be better (if you can find it) or perhaps hydrogen peroxide to sterilize the area. I had a hen once who was attacked by hawks, and she got stitches at the vet. Keep an eye on the wound. If infected, she'll need Baytril pills. A trip to the vet for an exam and Baytril would probably run at least $60.
If after she heals, you just toss her back with the others, she will get torn up again. If she survives that, they might accept her but it's risky. Introduction needs to be more gradual so they can see and hear each other before having actual contact.
I hope she gets better!