Children who will not accept instruction or correction or any adult guidance without having complete anger, management problems, or depression meltdowns

I have a six-year-old daughter who will not accept a yes answer at all. I can say yes we can do this or we can do that when we’re done with this or at a different time and sometimes even at that moment, she wants to have the complete control and authority of all things she will not accept a yes it literally comes to her beating herself in the head to get what she wants. She never get what she wants by the way when you go into a fit like that, I don’t continue to let you have what you want, that’s foolish and I don’t give into that type of behavior ever so just throw that out there that doesn’t happen in my home what does happen is yes I would love to watch your favorite show with you once we’re finished with Oliver schoolwork homeschool, and some chores before dinner maybe with afternoon snack possibly we’re gonna watch that together and literally I just had another complete breakdown from her because she wanted it with lunch While I made lunch and I said no, we’re not gonna do that but we will watch it in the afternoon and she wants to have. This is an every thing occurrence over everything I am at my utter breaking point.

She will not accept a correction I cannot go through any type of correction with her at all. It turns into a power struggle. Yes, a power struggle I know, right I should know better but I’m trying to plead with her, and then it turns into me manipulating to get her to stop and I tell her hey I’m gonna have to manipulate because you’re unwilling to control yourself or unwilling to listen or unwilling to do the good thing whatever it is, but I do let her know it’s manipulation, and I do let her know there is no other mother and if I was to leave, she has no other mother. She is not the mother there is no one to teach her. She is unteachable.

She does not need to be this way. In fact there have been many times she isn’t this way. I have an older teen daughter who is almost 16 she’s 15 right now who we are finding out is 80 HD and on the spectrum and higher emotional systems whatever all of that, and I’ve never been able to discipline her or correct her at all her entire life without her having a meltdown and screaming that she wants to die so this is what my younger one has has witnessed it is the worst and it affects my younger one greatly
I “we” are in a terrible crisis situation to say the least I’m not over exaggerating there’s so much that’s awful here
I love my family and seek desperately for God’s help. We are Christian.