Most of the times, when a young girl is sexually active, it is because she was either sexually abused by a relative , brother or father, or she has been emotionally neglected or abused by her father. I remember reading this years ago-- that there is a distinct link with having been sexually abused, or even just having a poor relationship with a father who is indifferent.
The young woman needs reassurance that she is loved in some way. Sex shows her that she is desirable.-- this equals "love" to her-- Love that she never got.
Both parents have something to offer emotionally for thier child. Many fathers feel left out when a mother dotes all thier attention to that baby, but the father is very much important in that child's healthy emotional upbringing.