Hey, my son is stutterer. 6 grade was the worst for him. Absolutely bad. He was new to middle school, kids at that age are mean, most kids had no clue what’s wrong with my son’s speech. My son had school provided speech therapist who worked with me intensively. However, not once did my son not talk to not present in front of the class. His therapist was god send. She made sure no one bullies him. It was a tough transition. My son felt isolated. But we kept encouraging him. Like your sister my son is also very very smart. He is now in high school. I’ve only made one thing the most important thing in his life, his studies. He wants to be a doctor and I think it’s perfect for someone who has first hand experience of dealing with a disability. My son had IEP in middle school which we strictly followed and more than anything what helped was advocating for him and teaching him how to stand up for himself. In high school he still has no friends but he is doing fine because he has a massive coursework, he plays team sports and volunteers on weekend. Tell your sister she has to keep going, tell her to dream big. These same people who may think she is weird will one day come to her when she is something. Unfortunately, these kids need to have skills that no one has and prove themselves to be the best at it. My son got a very competitive volunteer opportunity to work with children who require surgeries because he wrote in his essay about his speech which made him more empathetic and a great listener. Good luck!