Is she eating normal? Is she drinking normal? Sleeping normal? If so I would worry too much.
I can tell by her feathers she looks like she is a week behind on growing out feathers. But she looks healthy. Poop is a little runny but that could be from a number of factors. Just make sure she can get to water and food and is eating normal and drinking normal.
I had one that matured about 3 weeks after everyone. Didnt lay eggs till about a month after the rest. And became the matriarch of the flock.