I just got 3 chicks when they were 3 days old. They are now 7 weeks. These are the only chickens I have. The other 2 show no symptoms. The chick in question only shows the odd pupils (both eyes) and is smaller. I’m really hoping it’s some congenital issue. I will have to wait and see I guess.
Since you don't already have Mareks in your flock and your chick isn't acting strange (lethargic, having a hard time walking), I'm guessing it's normal. As for her size, we always have some that are larger and some that are smaller, even in the same breed. Keep us posted!