Replying to Need help.

Here's the story. This summer my best friend is taking me camping with her family. And also her dads girlfriend is going. We really hate her, like so much. She is the meanest person you could possibly meet ( like Corana Deville from 101 dalmations. So our plan is to pretty much kill her (not literally)....with pranks. Just like teribble ones. We already studied the parent trap (the movie) and got some ideas. We need something huge though, something really bad. please, ideas?