I don’t experience this with my parent, but I do with a really close friend. I’ve always thought it’s because I think they with this person it really doesn’t matter if I stutter, then I think about stuttering, which makes me stutter. I think it had to deal with thinking about stuttering or not stuttering more so with this specific person, this case your mother. I’m sorry I can’t offer much advice but just wanted to let you know I know and feel what you mean. I’d say to just not think about it but I know just as much as anyone here saying “don’t think about stuttering” is near impossible at times like these.