She may be trying to help in her own way by trying to build up your confidence. I agree that you should talk to her about it. But I also don't think it would be healthy for her to step in and talk for you. For me at least, the most positive situation is when my SO hears me stutter and struggle then just looks at me and I know she is not shaming me. She could care less if I do or not but she also wouldn't step in to "save" me