She probably just got hurt by the dog. You'll want to clean the wound and use neosporin on it. As for her leg, maybe she got it caught when jumping or the dog injured it. If she's limping, that's better than not using it. So take comfort in that.
She'll need to be kept separate - maybe with a buddy or close to her other buddies. You'll have to make sure she keeps eating and drinking. She's very young and dog bites are nasty, so keep watching her wound and keeping it covered with antibiotic ointment. IF there are flies in the area, bring her into a brooder inside. She should incidentally be eating chicken starter crumbles at this time - is she? And what are the little ones to which you are refferring? Another batch of chicks?
She probably just needs time to heal, during which as I said above she needs to be kept a little quiet, and needs to eat and drink the normal good food she eats and drinks. I wouldn't even give her vitamins/electrolytes at this point, certainly NO antibiotics.