Wow. Is there any way you can send her articles on stuttering, for her to understand that stuttering is a neurological problem that you can't help? She seems to be one of those ignorant people that thinks stuttering is exclusively a problem of being nervous. While being nervous can exacerbate a stutter, it is not the root cause, which is where she's getting it wrong. I'm assuming you're in university. Stuttering is considered a disability. You can talk to your university's disability services and negotiate accommodation. You can try to get out of doing presentations if you would like. I personally would not reccomend that, as I think avoidance only serves to build anxiety, fear, and low confidence. You can, and should, use the DS to highlight that it is a neurological disorder. I would hate for you to get docked marks off of a presentation because of something out of your control. Emphasize that you cannot control it, and the professor should be paying attention to what you are saying, rather than how you say it. To grade you on the merit and strength of your argument, not how fluently it comes out.