I think you should address her directly instead of going to HR/higher management so that you don’t risk making your career complicated or messy. As much as it sucks, it’s not severe enough for them to fire a manager on the spot (unless there’s a group of other people also coming forward). She’d likely get a warning and then you’d be stuck with a boss who knows you complained about them to HR/their boss. And we know how that’s gonna go. It’s total bullshit I know but by handling it head on it gives you a chance to handle the narrative. Maybe something along the lines of “Hey, I just wanted to let you know that I have a speech disorder which occasionally causes me to stutter or freeze until I’m able to get my words back on track. It’s completely out of my control when it happens which is why you may not notice it in some conversations. When we first met i didn’t appreciate the mocking of my stutter, and i just ask that you treat me with respect and wait for me to finish as I do for you. I’d love to put this behind us and start fresh.” But this honestly all depends on her demeanour like if she’s rude or unapologetic then make it firmer but if it was genuinely a mistaken ignorant comment it could be a good opportunity for you to educate. Then get a name card 🤣