NTA, but skipping the wedding is a bit much.

My daughter hates her hair and expected a pretty bleach blonde “like Billy Eilish” which is what her grandma promised her, not a faded mess.

Sounds like your daughter was on board with bleaching her hair so while you're definitely justified in being upset that your mom kind of went behind your back and then used a bad technique, I think your reaction might be a little over the top.

Did you tell her that you were planning to change your daughter's hair color? Did you specify that you wanted to do it a certain way?

If not, and with the fact that you already change your daughter's hair color semi-frequently, it kind of seems like it comes down to miscommunications and assumptions.

I'd say you'd be justified in asking your mom to pay for fixing your daughter's hair, but skipping the wedding is excessive.