First off let me say I'm sure I'm in no way qualified to give advice on parenting a teenager. I feel for you. Especially at that age some girls can be really hard to connect with.

I gather from your post that its mainly sex that you're worried about? Or is it other issues as well?

Discussing contraception with your daughter is a really good way to bring up the issue (I assume you're referring to implanon?) but I think it's important that your daughter feels actively involved in the decision making process, eg going to the doctor to get information together etc. Also, don't forget how important it is to discuss stuff like STIs, HPV vaccination etc. Most teenagers are as scared about getting pregnant as their parents but I don't think many of them realize how common STIs like chlamydia are and the potential long term effects.

What's your daughters relationship like with her older siblings? Don't forget they could be your best allies if she's not willing to open up to you.