Even people who aren't stutterers still sometimes stutter, especially when nervous or anxious. It's rare, but not unheard of for people to get late onset stuttering after they've grown. Even if you don't actually have a stutter, the psychological concern coupled with the fact that your mom responds to it by scolding you and accusing you of faking it is wholly unacceptable and problably the worst thing she could do. I dont know if she's the type of person who would listen to telling her not to do that, but you dont want that worry in heard head each time you open your mouth. If you can't talk about it with her directly, maybe you can talk to your dad about it and he can explain it to your mom. You don't need anyone turning this little thing into something more.