I think she has sprained her leg. Usually when this happens the chick will heal by itself if left in a smaller brooder with soluble vitamins. But if she is holding her leg out to the side you will need a splint, for adult birds a piece of hose is ideal if they've broken their leg, however, chicks are too small. An easy way to hold her legs in place while she heals is to use medical tape. You simply put tape on the injured (just above the foot) leg and stick the other end to the good leg so that there is the normal amount of space between her legs (we do this with splay leg chicks). She will have trouble standing at first but will get up eventually. It is best to take this chick to a vet for an effective recovery. I hope your little one improves.