What do I say to her?

I have a toxic friend who I don't want to be friends with anymore but she does my head in and o cant stand her . She tells the teacher off everything and the teacher goes to ke one more complaint even a little one I will bring your parents in to guide you around school . This girl has told meoff for everything buy these were petty issues and the teacher said that . The girl makes me wait for her after class so we can walk together we are in the same class and we come out together . I don't wanna wlak with her so I'm just going to walk away from her but the problem is the next day she will ask me why I didn't wiat for her and idk what to say because please remember nothing bad as dhe will tell off me and I cant let that happen. Some of you have already said that I cant get into trouble for not waiting for someone but the teacher said even little issues and she will call my parents in and that girls tells off everything and I mean EVERYTHING. So when she asks me why I didn't wait for her what do I say