My mum, too, made decisions that I feel threw me under a bus (figuratively speaking).
It might be that your mum avoided putting you through those dental processes because she thought it would all be overwhelming to you. If this was her reason, she was misguidedly trying to spare you from one trauma, although it set you up for a different kind of upset later on, in that you now are not happy with your teeth and it's too late for it to not cost the earth to fix.
My mother did the same kinds of things -- believing she was sparing me from something I would find upsetting at the time, only to set me up for worse consequences later.
I think these things are done out of genuine caring but poor insight into what happens later down the line.
Of course this is only speculation -- she may have felt it was too expensive even when you were a child.
It's really hard to let go of things like this, I know because I have a bunch of these things in my life too, regarding the decisions of my parents.
I can't tell you to get over it because there are ways in which I haven't really gotten over mine either. Sometimes you just have to put it aside even if you never really stop feeling upset when you do think about it.