I believe (could be wrong) that the title of Snow Queen came from Disney costuming. Just like the The Prince from Snow White is referred to as Snow Prince. They put the 'Snow' there to denote that the character is from Snow White. Now, I think it would have been better for Regis to have said "That's the Evil Queen from Snow White" but since I've heard the title of Snow Queen I didn't think anything of it. Disney doesn't market her as Snow Queen, but I heard about the Snow Queen name for her from a Disney employee, so I guess maybe it's just a thing used inside Disney.