I think Rapunzel because she would remind her of the younger sister she never got to play with while growing up, and her love and insecurity would definitely make Elsa feel sisterly towards her.

She takes her priorities seriously, just like Elsa. They are similar, and would be great friends, imo. Also Rapunzel.

or cinderella or snow white or belle, their all very classy and responsible

I think they're very similar actually. That's why they're my top 2! :D

Cinderella would be second, and Belle would be third. She's love Snow White as well.