Aurora most likely, it would probably be the same thing as it was with Flora & Diana, Flora is an experienced and high levelled fairy of nature, but because Diana was the major fairy of nature she had a stronger and more fond bond and connection to nature than Flora did.
It would be the same with Icy & Aurora, Icy is a very skilled witch yes, but we know for a fact now that she isn’t a descendant of an ancestral witch and we can’t be sure how strong her family tree is, none the less, Aurora being the major fairy of ice would have better control and stronger powers and skill over Icy no matter.
Just a thought.