~ Chapter 16 ~ Why does Catherine get angry with Kristi?

The next day, Kristi comes over and the girls draw posters for the dance together. David comes in the room, and Kristi gets the idea to teach him to dance. Kristi turns on a music CD and Kristi and David dance in their own way, with David stepping on markers on the floor. Angered, Catherine turns off the music and accuses Kristi of mocking her brother. Kristi responds that she was only letting him have fun.