Coming to terms with your past is an ongoing process and not something that you ever finish, even as an adult! Your perspective on the past changes as you grow and mature.
Thinking that one's negative feelings about past experiences can be laid to rest once and for all is black and white thinking, and just not true.
If someone's past is keeping them from thriving in the present, they should see a therapist to help them facilitate the process of working through it. But it's not a process that will ever have a clear endpoint, and it's not your responsibility, OP.
Your DD seems quite controlling. She needs to come to terms with the fact that all of us control our own actions, but not other people's. She needs to accept that she's an agent, and take responsibility for making the change happen that she wants to happen. She can't rely on other people to change their behaviour; ultimately the only behaviour she can control is her own.
Good luck and I think you're doing very well with parenting an ND child. It's a shame that she sees autism as such a negative label. I have friends with autism who are Oxbridge professors... autism is not something to be ashamed of. In fact given that many of your family members have autism, she's insulting you by saying it's such a terrible condition! It's just one mode of being human. Neurodivergence is not in itself a negative thing!
I don't think you did anything wrong making her get a diagnosis either, when she was young. Parents have to do what they think is best for their DC. You were doing what you thought was best for her. You shouldn't blame yourself. It's a bit mad that she is blaming you for the diagnosis, when what she wants to do with the diagnosis (disregard it or not) is entirely up to her. She's an agent!
Ironically the black and white mindset of 'my diagnosis is a lie!' is actually further evidence of the fact that she's neurodivergent, because she's placing so much importance on that label. Honestly who cares?! Some of us who are ND find diagnoses helpful, others don't. A diagnosis does not need to affect your life unless you want it to.
So yeah, stop blaming yourself and encourage her to take some responsibility for her own happiness.