I am studying psychology and well yes, what she is doing is really bad for your self esteem and your view on your stutter. Our stutter isnt something we can get rid off. The reason we stutter is biological. And it gets worse when we are mentally feeling sick or bad. My advice would be to sit down with her and talk about what you are feeling and how its affecting you. If she loves you, she will try to understand and change the way she acts towards your stutter. You are brave for practicing and never let your stutter hold you back from anything in life. We are all here to support eachother and know that you are not alone. Goodluck!!!!