I'm with Donrae on this. She looks to be about 5 months to me based on her comb development.I agree she's an easter egger hen, but I'm not sure she's that old. The comb doesn't look very red to me, meaning she's not laying. She doesn't look like she's molting, so my thought is she's just too young.
I think she'll do fine with your birds, but it will probably take weeks for her to settle in. Lots of time, a fair amount of food, and she'll be just one of the girls.