Ana/Mia jellies only: If your friend knew about your ED and was using it against you (black mailing) what would you do?

My best friend knows that I have an eating disorder and every time she sees me heading to the bathroom after a meal, she gives me a look that tells me she’s considering telling my mother. She uses it against me when she wants me to do something or wants me to tell her something and I’m really scared that she’ll tell someone and I’ll get caught. I don’t plan on stopping anytime soon and I REALLY don’t want my mother to find out. I can’t erase her memory but I know, despite her promises, she’ll end up telling someone eventually. It’s not serious, it hasn’t been happening for very long but when she found out I made her swear not to tell anyone but now I’m worried she’s going to go back on her promise. What would you do in this situation?