Imo the author amping up Sasha behavior so the twist would be more impactful is completely unnecessary! I don't know what bs "their" parents did (we saw Sasha imprisoned in some dirty dungeon), but Sasha doesn't trust anyone and will trick anyone even making them believe she's a bitch just to save her sister! The kiss (when he reads her thoughts) is the prove she plans to have Misha live and she will disappear! That's why she probably needs the scepter!