I have Aya with a 65% Ranked Froslass and she has still not transformed into Aya Rank II. I am currently doing Legend of Ransai and have all kingdoms except for Spectra.
You can only evolve the main character during the Legend of Ransai story. otherwise you've met the requirements but sadly you'll have to re-level the froslass again.
I know this doesn't say anything about that, but it should still help in the future.