How do I make my mother understand that I do not stutter voluntarily

How do I make my mother understand that I do not stutter voluntarily Hi as the title says. For context I (24F) stutter since I began to talk, but now I manage to mask it so it's only light stutter unless I get upset or any other emotional change that makes it more obvious. When this happens when I feel upset or angry my mother teases me saying that I do it on purpose (stuttering). This drives me nuts and makes me feel awful. I have been to speech therapy as a kid and my mother still doesn't believe that I'm a stutterer. I feel invalidated basically. Can someone give me advice? Thanks