none of them, honestly, because with her slightly awkward, shy, very introverted personality, people like her just typically have a hard time fitting in. not for a lack of trying on her part, or because they would dislike her (some like Snow not understand her maybe though) or hating them for being "ew girly" like the worst of her fanbase thinks, she is just one of those people who doesn't form close friendships easily because of her different personality and introversion.

But Poca she'd understand the most and vice versa. I think she'd get along with Belle, Cinderella, and maybe Tiana too though. she just wouldn't be super close with anyone. And I don't see at ALL where everyone sees a close friendship between her and Merida. They have nothing in common but fighting skills and even those are for totally different reasons (fun for Merida, necessity and nothing else for Mulan). Fire and ice. Mulan doesn't prefer to defy tradition, she just does it if she thinks she has to. she was fine with arranged marriage. Merida, of course, is not that way at all.