Really annoyed that someone made fun of my stutter

Really annoyed that someone made fun of my stutter Hi guys! Okay so I'll try to keep this short. Basically, I have a stutter but I haven't been diagnosed. I repeat syllables, words, get complete blocks for a couple of seconds and sometimes even say things that are straight up unintelligible (e.g. instead of saying 'make sure you're okay' I'd say 'mshdkssure you're ok...ay'. This usually isn't a problem, it's not like I stop speaking because of it or anything. However, this week, I was talking to some of my friends and while speaking, I kept repeating the first letters of the word I was trying to say. I only did it like 2-3 times but this girl in my friend group who I'm not even that close to goes 'buh bUH BUH' (i was repeating the letter b) and then says 'wait you stutter, omg i didn't know you stutter?' in this annoying mocking tone. I literally gave her the dirtiest look and told her that yes i had a stutter and even my other friends told her that it wasn't something new. The girl then gets upset and walks away because her 'mind decided it wants some me time' Apart from the fact that I'm annoyed at her, like, she made fun of me, didn't even apologize AND went to sulk only because I confronted her, I'm also now more conscious of my stutter (my friends admitted that they noticed it and someone else mocked me for it yesterday even though that same person said that it wasn't that big of a deal before). I don't really know where this is going but every single time someone makes fun of my stutter i get so upset. Am I overreacting? What should I do to stop?