“I’ve asked you twice to read your book. If you don’t finish that chapter in the next 10 minutes, Maria can’t sleep over tonight.”
Many parents explain consequences this way—and that’s fine. But remember that it’s important for parents to mean what they say.
If you know that Maria will be spending the night—no matter what—due to an earlier family arrangement, choose a different consequence.
Your child will be more motivated to behave—and more likely to take you seriously in the future—if she sees that you mean what you say.