Is your daughter in a special education public school? I wish there is a charter school for autism near me, but there are several private schools for the low end of the spectrum not far from where I live. My son gets bored fast in a public school. He is strongly mechanically inclined, so he prefers to work with his hands. It is one of the reasons we put him in a private program to keep him engaged. In Arizona, there are charter schools for autism, which is nice.
What hereditary does your daughter have? I have read similar cases like autism and intellectual disability in Nemechek Facebook groups. Intellectual disability is not a cure, but the protocol help their kids function better. It is not perfect. Several parents mentioned that their kids with intellectual disability and autism were nonverbal or nonspeaking until they put them on protocol. The kids became more aware and are dealing with new emotions they did not recognize before. Actually, they are overwhelmed and become hysterical so hard. And some of them even start to speak. Parents have LOTS of patience to teach them how to deal with emotions.
Sorry about your sister. It sounds like you're a carrier and it could possibly be both of your parents, too.