I'm really sorry to hear that your sister reacted in such a way. I can understand why you may feel like that one interaction halted any progress you've made. I do agree with what someone said below, that of all people, your family should understand your struggles with stuttering/stammering and show you patience. Have you tried sitting down with her and explaining what you have to go through on a day to day basis to manage the stutter? I'm in a situation where the person I talk to the most is my brother, and he has a stammer as well, which used to be much worse than mine. My stammer used to be so bad that in class, I would get so anxious knowing I would have to read out loud that I would sometimes get light headed and almost pass out causing more attention to be brought to the situation. I did have a similar experience with a coworker however, and it hurt. It was someone who I never thought would make fun of me, but I was wrong. What made it worse is that I called him out on it in front of about 10 of my other coworkers and the awkward tension could be cut with a knife, but I felt good for standing up to myself. I hope things get easier for you soon. Remember not to discredit all the progress you've made so far.