What should I do when my friend does this again?

Recently one of my friends has been really annoying me. She's been telling personal things about me to other people indirectly in front of me. I had a boyfriend (now ex) and i gave him a *******. I didnt even tell her. She found out by asking me "oh did you give him a *******?" I said yes bc im bad at lying and didnt want to lie anyways. I thought I could trust her bc she said she wouldnt tell anyone. However, she always, in front of other people, asks questions like "so did you give him a handjob?" or "would you hook up with him if he wants to now? And the friends that she does it in front of are our Christian friends or a large group of friends which includes one of the guys i had a thing with a long time ago. Some of them probably already know that I gave my ex a ******* bc her brother (my ex's close friend) did the same thing to me (ask me questions that i cannot say no to then tell everyone else), but I dont like it when she does this in front of people. I feel like if she does it again, I will blow up at her, but I still want to be friends with her bc im not that type who likes to bring up fights. I do joke about sexual things when we talk about it or when funny things comes up in front of other people, but thats different from taking things to the personal level in my opinion. Im trying to act chill about it while showing slight frustration, but she does not seem to get it at all. What should i do? Thanks in advance.