I feel so guilty looking back at how I treated my daughter for the past 21 years

I don't even really know why I'm posting this, I think I just need to get it off my chest.
My daughter is 21 and she's recently been assessed for autism. We've been told she meets the criteria, and honestly, it's like someone has finally switched a light on after 21 years of us stumbling around in the dark.
So many things suddenly make sense.
The school. The absences. The meltdowns. The exhaustion. The jobs she loved but couldn't keep. The things she couldn't seem to cope with that other people seemed to manage so easily.
And I'm sitting here thinking about all the times I got frustrated with her.
All the times I said things like "why can't you just..." or thought she wasn't trying hard enough.
God, I feel guilty.
Because she WAS trying. She was trying so hard and I just didn't understand.
I thought I knew my child. I knew she was sensitive, I knew she got overwhelmed, I knew certain things were harder for her. But I never understood why. I didn't have a name for it.
And when you don't understand something, it's very easy to get frustrated by it.
That's the bit I'm struggling with now.
I keep thinking back to things that happened years ago and seeing them completely differently. Things I thought were bad behaviour, laziness, stubbornness or her just not wanting to do something.
And now I'm wondering how many times she was actually completely overwhelmed and I just didn't see it.
I wish I could go back and tell her I understood.
I wish I'd known.
I'm not looking for anyone to tell me I'm a terrible mother, because I already feel guilty enough. 😂 I just wonder if other parents have felt this way after their child was diagnosed later in life.
That horrible mixture of relief because things finally make sense, and guilt because you're looking back thinking, "Jesus, I wish I'd known sooner."
I love my daughter more than anything. I always have.
I just wish I'd understood her better.