The key difference, is you haven't left.

How can I tell her it's not "too little too late". I know that she's thinking "sure, you do something about it now that I have left, why didn't you do something years ago".

What can I do? I'm slow, but not completely dumb.

I'm reading books and improving myself. Yes, I should have done this years ago. But today is today. I can't change the past.