You should sit it down and have a heart to heart talk with her. Communication is very important so that she will know that you are there and even though it would be awkward to answer questions about it, you still need to discuss it. Tell her about the limitations and most specially tell her about the risk of being sexually active, give her information such as the diseases like STD, HPV, AIDS, HEPA-B and the risk of being pregnant at a young age (the responsibility and dangers of delivery). They key is really to discuss/communicate/talk.