I have a couple of sebright pullets that are 32 weeks old and have not started laying. Most of my bantam pure breeds begin laying around 6 months old, but because this time was in autumn, the days were too short already. I'm hoping they will lay in the early spring. I've had pullets in the past not start to lay until almost a year old.
Having said that one of those (a Pekin Bantam) must have had some kind of hormone imbalance because for a few weeks around 9-10 months, she crowed or tried to crow on occasion. Then at, almost 12 months, the first egg came and the crowing stopped. She hasn't crowed again and has gone to to hatch and mother chicks with no problems.
Hopefully your pullet will start laying in spring. I wouldn't worry about it if she is otherwise healthy.