You might try counseling to help you move forward in this relationship. In the meantime, respect her decision to wait. It doesn’t necessarily matter why she’s decided to wait, it only matters that you respect her decision.
You both are still developing and maturing. The teenage years are chaotic because people are going through a process of learning about their true nature, who they like, what they like, what’s right for them, etc. She has done nothing wrong.
Don’t pressure her to do anything that she is not ready to do. It’s best to be respectful and allow her to do it her way. If you don’t like her choices, then perhaps she is not a match for you. Counseling could help and I suspect would help, a lot. Thanks for your question. Good luck and please take care.