How to communicate with my sister

First of all, you can't tell her by order.

Talk to her more and see what she thinks. Be comprehensive, such as making a study plan, so that she has little time to think about other issues.

Eliminate her curiosity (between men and women) in an appropriate way. Euphemistic and concise explanations should now focus on learning. Even words like examples and methods can tell the truth and reduce her curiosity.

Spend more time with her (study, outdoor activities).