Behavior is a language, and her parents are acting as if they want her to move out.

If your parents are asking you to pay rent to live in your childhood home, there’s a good chance they don’t even want you to pay rent and just want you to move out. Many parents are willing to be a soft place for their adult children to land when they’re going through hard times, so they allow their adult kids to stay at their home rent-free as long as they need. That works well if their adult kids desire to be independent, and would only move home in the worst-case scenarios. That works less well if their kids are willing to leech off of them for their entire adult lives and don’t feel a need to support themselves. 

The period between graduating from high school and attending college is usually when parents are most comfortable with their adult children living at home. After all, it takes income to support oneself, and a high school graduate is going to have a more difficult time supporting themselves on their own than a college graduate or an adult with a couple of years of work experience already under their belt.