Hi Katie,
Does she live with you? If so, close the bedroom or even bathroom door after fifteen minutes of this nonsense.
If she doesn’t listen to you, you can: “forget” you were supposed to meet, say you’re “busy”, arrive late, leave early, not answer every text, not return every phone call, answer multiple texts with one emoji, cut the call short.
If you want to have fun, tell her that every time she badmouths another girl you’re going to take a drink. Turn it into a drinking game! If you’re not old enough to drink, just play with your phone and mutter, “Go on, I’m listening” when you clearly aren’t.
Drive her crazy: Tell her you’re entering a beauty pageant. Do it! There are many “average” girls who enter, actually.
Tell her you’re modelling for a local company. Do it! Local businesses love familiar town faces in their ads.
Tell her in front of your whole family that you love grandma’s nose and how you love looking like everyone else in the family. She will see that the people who matter love you no matter what.
Good Luck!
Inky