Why hasn't my 15 year old girl hit puberty?

Familial?: At what age did you hit puberty? Do you see any signs of her body changing? Breast development, pubic and axillary hair? Has she seen a doctor on a regular basis who has tracked her growth and development?

May be ok,may be not: Familial delay is most likely(when did mom enter puberty). How is breast development, axillary and pubic hair, body odor? How has growth in height and weight been progressing over the years? What is height of mom and dad and the height of your daughter? You need to go to your pediatrician who can do further testing, bone age studies, etc, if concerns remain.

Hard to say: Your question has no real detail on which to base an opinion. Do you mean no findings at all ? Nipple growth but no menses ? Were you late to develop ? A girl should have nipple enlargement by 13 and menses by 15.Sometimes family patterns result in late development, but by 15 she should be evaluated to exclude medical problems.