Anna could just have a sheltered upbringing, super naive, but very preppy and outgoing to compensate for the lack of outside interaction. Both she and her sister could have been home schooled up to this point. Similar to Rapunzel...who could also be their cousin, according to the famous head-canon XD

Had the same idea with Mulan and Alice XD but I'd do a 1x1 if not too many people want in on this and you guys are still up to a group rp I may take on 2 chars