If Zhenya grew up with Elsa (in Arendelle) life would be easier for Elsa, but worse for Anna. Elsa would not have been so isolated; she and Zhenya would have been isolated together and made snowmen all day in their room. (Origin: King Agnarr and Queen Iduna found out about another little girl with ice powers and took her in so Elsa would have company, and maybe learn to better control her powers.) But then, not only would little Anna be sad and lonely she doesn't get to spend time with her big sister, she's also jealous this new girl gets to spend time with her sister. So Anna starts to do reckless stunts to get attention, like riding her bike down the hallways without proper head protection. And talking to inanimate objects. Eventually she decides to run away. She meets the trolls, they take her in, and she has random adventures with little Kristoff and Sven. Because of cute. Meanwhile, back at the castle, the king and queen notice Anna missing so they leave to search for her.. and they are never seen again.... But anyway, Elsa is less reserved with Zhenya, and more open to using her powers and testing them out because she knows they can't hurt Zhenya the way they did Anna. They grow up and Elsa becomes queen and Zhenya her royal adviser for a short time. She gave great advice on how to fix a problem, but she overlooks that people have different needs and emotions. The people of Arendelle are safe, but unhappy. Elsa notices, politely fires Zhenya (even tho she literally doesn't care either way; no emotions of her own) and Elsa finds a nice balance of safety and pleasure for running her kingdom. Eventually Anna comes back tho. (I don't how, but the sisters need to be reunited. Elsa loves her emotionless companion, but Zhenya is no good substitute for a loving little sister.)
If Zhenya grew up with Elsa (in the Tundra) it'd be the same about Elsa embracing her powers, only more so. She'd be completely free and never have to hold back, and learn to control them pretty early on in life. (Origin: I don't know how Elsa ended up at the North Pole. Maybe she got lost looking for Santa? Or maybe the king and queen feared her so much in this AU, they sent her to live as far away as possible? Then Zhenya, being the only "human" around for miles -and being incredibly lonely- lets Elsa live with her) Back in Arendelle, the king and queen feel sad and guilty about losing Elsa, they shower Anna with love and attention, and she would be the happiest little girl in the world!..if she weren't haunted by vague memories of an older sister she hardly knew. While back in the Tundra, Elsa is happy to be free to be herself and even tho she has Zhenya, she still misses her little sister, but is afraid to return to her; afraid she might hurt her again. So she projects all her big sister love onto Zhenya..who tries to return it, but, Zhenya just can't do emotions. But good news! (not really) Spejl (the mirror demon) shows up. (Zhenya lets him stick around in my story because she's so incredibly lonely, literally anyone's company will do. But if she has Elsa for companionship, she wouldn't care about keeping him around, tho she wouldn't kick him out either - but Elsa would!) Zhenya doesn't care, but Elsa hates Spejl and they often have ice/mirror fights. During one of these fights, one of his mirrors is broken and a tiny shard finds its way far~away and into a little boy's eye. And that little boy becomes a jerk towards his best friend. But luckily for his friend, Zhenya doesn't kidnap him in this AU, because with Spejl and Elsa around, she's not lonely. So the friend doesn't go on a long arduous journey to save him from Zhenya. But she still has to save him from the mirror shard somehow because, let's face it; I love you, Kay, but you're borderline useless without Gerda. xP
Only in the second AU would Kay be effected by the mirror, but in both AUs, Zhenya would not kidnap him, so Gerda would never have her own adventure. :(
Bonus: since Gerda never met Danika (the robber girl), Danika never turns her life around. So she grows up to be a notorious bandit who ends up mugging Prince Hans and taking over his brothers’ kingdom. >xD
