WARDED TO GIA
I'm sorry to intrude, but I couldn't help but read the conversation between you and your sister. It might actually do more harm than good to try and 'lock someone up' for urges or questions. It could backfire and lead to things like diseases and pregnancy due to unprotected sex. Not to mention the psychological ramifications of rushing into it to spite people.
If you don't mind my offering advice, I would try and answer any questions she has and then explaining to her the risks of going into it before she's ready, but also pointing out the things she can do to protect herself if she is ready.