youdontknowme I have some other words on her mother's authority, but I want a real keyboard before I put them to bytes.
So, to get back to this:
The girl is 18. Legally an adult. She is free to make her own decisions, and her decisions are no longer her mother's responsibility, nor subject to her control.
If she were younger, her mother could discipline her in ways that do not involve interfering in her bodily autonomy.
If she wants to be a slut, that is her goddamn right. Any right of her mother to interfere in this can only be justified by either her consent or a psychiatric and/or judicial finding that she is unable to make decisions that do not cause harm to non-consenting parties.
That said, I also believe that her mother has the right to incentivise that consent to a certain degree. Obviously not by withholding any basic care like providing her with food, shelter and education until she can be expected to take care of that herself, nor by taking away property that was already hers, but if it is access to luxuries or something like that, I think it can be justified to at least some extent. Not saying free rein to demand anything in exchange for basic human decency of course, but I can understand if Monica does not want to support Jane's lifestyle when it runs so contrary to her own beliefs.
The car is an example of that. If it is owned by the parents and loaned to Jane (or provided to her under some condition), taking access to it away if she does not give her mother some way to ensure she is not driving it to a sex date seems like an acceptable deal. If it had been gifted to Jane and is officially hers now, things would look different.