chicken hasn't started laying

[crazychickenwoman]

I have a nine month old new hampshire/rhode island red hen that hasn't begun to lay yet. All my others (different breeds) layed at 16 weeks. Is this normal?
I've noticed that they all lay in the one nest even though they have several to choose from. Any suggestions would be appreciated.
Thanks

 

[FamilyOfChickens]

Could be a number of reasons...Maybe she's laying them, but they're getting cracked by all of them in the same nest. Could also be because of heat stress. Is she eating oyster shells along with the layer feed?