What should i do?

one of my friends who is an adult found out that I had oral sex with my boyfriend and now she is mad at me. she wants to talk to me to find out why I made that choise to do that but the truth is, I really dont want to talk to her about that I would...

rather text her. what should I do/ because I really dont want to talk to her about it, and I dont have a choise, I have to talk to her or she will tell my mother and I dont want her to do that

It's none of her business really and she should respect your personal sex life. You have a boyfriend and you tried some sexual stuff with him. As far as I'm concerned you didn't do anything worth her getting into a fit about. I think you should ask her why she is so interested in your sex life because frankly it's none of her business.
Is she is trying to warn or protect you? In this case she should say so clearly. Just talk to her and be honest about not wanting to discuss your sex life with her (you are allowed to keep this to yourself). After all how would she feel about you asking her about hers? And ask her why she is getting so upset and why she wants to tell your mother. BTW, how did she find out about this in the first place? You might want to think twice about who you tell about your sexual experiences.