AITA for not wanting to talk to my friend after she told our orchestra director my personal things?

Hi so my friends are angry for not wanting to talk to our mutual friend let's just call her Mik. Me and Mik have band and orchestra together and are pretty close since we were the only "band nerds" in our group aka we were the only ones in marching band. Ive been dealing with health struggles and needed to go to the hospital a few times for testing and things to get diagnosed (still not btw) and I needed to tell my band director since I had to tell him my medications and that I needed an inhaler with me 24/7 since I needed it for my marching band forms. I was regularly updating him about it, and i also told Mik about it a bit because i was worried about it obviously. Well one day I told my band director that I wouldn't make it to practice that day since i was leaving mid school day to go to the hospital for tests and that I would email him or something. Mik was standing next to me and so was our orchestra teacher who stood next to my band director. Our orchestra teacher just stared at me a little wide eyed but I kinda ignored him because I had to go somewhere after that and because it didnt concern him and I didnt want him knowing all my business. But, Mik smiles, kinda giggles, and looks at our orchestra teacher and says "oh its just something about asthma" and like just telling him the things I've been needing to do.? I didnt say anything but I was pissed because I didnt want him to know that. Ive been kinda avoiding telling her things now and our friends have started noticing and they keep telling me that im being rude even though I told them what she did. It's only been a week but they're starting to make me feel like a jerk and that I shouldnt be mad at her. AITA?