It is wise to give all teens access to choices for birth control because they sure have access for places to have sexual encounters. Places many older parents might not consider it would be an issue. Like in the Mall, the park, library, church campus, and school campus.
There is not always strength in numbers and in fact often there is prssure to have group sex. Or sex for "peers" to watch.
I would strongly encourage giving teens a dual approach at birthcontrol. Ignoreing the fact that sex is not always a "choice" for teens is also something to keep in mind. That can be from rape to subtle long term persuasion; especially within a relationship where one is submissive or dependent for one reason or another. Maybe it is for use of a car, cell phone, or even retaining a job or a secret.
What concerns me is why is a child in the custody of a parent who is so intimidateing that a young adult can not at least talk about something so basic as reproductive health or going to her pediatrician for a confidential check up, information, and birthcontrol which is her right to ask for.
Hopefully she is getting opportunities to get approval and acceptance in other areas than sexual activity.
I can't help thinking this teen is ALSO trying to manipulate her parents into negotiateing and communicateing her needs with each other. Tough responsibility for a teen with many other things to be coping with. However going to a non custodial parent for so obviously a "hot topic" suggests someone is playing the ends against the middle and maybe jocking for living with the most permissive parent. Allowing yourself to be played into keeping secrets from the custodial parent rather than closeing ranks and alerting him that a 16 year old minor is being pressured for sex is cutting your child's nose off to spite your ex's face.

Good post, lots of common sense.
Also not notifying custodial parent could bring a law suit.
Loss of visitation rights?
walk carefully