Should I be worried?

This is our first experience raising chickens so I'm trying to learn as much as possible. We got 4 chicks about 10 days ago. A Black Star, Ameraucana, Delaware and a Brown Leghorn.
The Black Star is a little bit older so has always been bigger. Now it seems they are all growing well except the little Ameraucana. She eats, drinks, poops, scratches, etc. But she isn't quite as lively as the other three, she stands with her eyes closed more than the others. Sometimes she sleeps by herself while the rest are together, but it seems like she's trying to buddy up with the Delaware. The other chicks don't peck or bother her. If we hold her she will walk around and eat scratch from our hand.
She just seems sleepier and slower to develop than the others, more fluffy, etc.
Does that sound like there could be something wrong with her?
Thanks!