one hen not laying

[chickbliss7]

I'm stumped as to why one of my mixed breed, 10-month-old hens hasn't laid an egg, whereas the rest of my girls have been laying for months. She's a Barred Rock, my largest hen and seemingly very healthy. Could I have a hen that can't ovulate? Is it possible she's a late bloomer? She's one of my friendliest, likes to be held and sits in my lap. She's also the dominant one, and will mount the more submissive hens. I'm certain she's not a rooster, but what's up with her?!