I think rehairing her could be a fun project! I’ve always been bothered that Rainbow Dash doesn’t actually have rainbow hair lol so you could make it right! Getting stuff out of the hair is tricky, I don’t blame you for just chopping it off. You have it a fair try!
I do have a friend on the other side of the US that might want to do it. I just have to ask her first.
I agree, like why does Hasbro not do the manes in any of their G4 ponies actually accurate?! It really makes me overthink it.