Edited because I was replying to a now (thankfilly deleted ) post. But I'll leave my thoughts here
Why are you so determined to vilify autistic children? Attitudes like yours cause much greater damage to struggling families than any diagnosis.
Coping with complex and severe disability in all its forms impacts families! Families are "destroyed" not just by autism FFS.
But sticking to this specific thread, the OP describes how her dd holds it together at school but has meltdowns at home after school. So, straight away, despite OP saying the SEN support in school is good, there is concrete evidence that it is not meeting her dd's needs because the child is dysregulated to the point of meltdown as soon as she leaves school! That's why we're saying discipline won't solve the meltdowns at home!
Getting the education that her dd needs would be the first and most important type of support that would have a massive impact on the family.
But the reality is that because she's experienced the wrong approach for so long, trauma is being added to primary neurological disabilities. And there is virtually no specialist educational provision for children like this.
I have decades of SEND experience as both a professional and a parent. I am fully aware that some disabled children have needs so complex that living for some or all their time out of the home is the only way to meet their needs and in some instances keep family members safe.
But there is so much in the OP's posts that indicates that the crisis has occurred because the child's needs are not being met first and foremost at school.
Families and the SEN teams in LAs need much greater knowledge and understanding of the different approaches that are needed for a child like OP's dd. Complex needs but cognitively able. Especially when possible PDA rather than typical ASD.
Parents get a diagnosis (asd, adhd etc rarely pda) and then very little support afterwards. Parents spend hours seeking information and understanding alone on the Internet.
My experience of CAMHs is either they are not equipped to work effectively with most ND children who get referred to them. And in patient facilities and even worse.
Social care are geared up for safeguarding or more 'traditional ' types of disabilities. Getting funding for holiday or afterschool support for cognitively able ND children is almost impossible.
So there should be avenues of support for the OP's family thst really could make a difference, but instead they are left to reach crisis alone.