DhampyrX2 said:
Belle is arguable. She came to live with him under duress and you could argue Stockholm Syndrome with her but it was more of her changing him and bringing out his good traits ala Wuthering Heights than "Here's this guy who I saw once by a well then kissed me while I was in a coma. I must marry him." It's an older idea of romance, certainly, but it was much more story driven than the original three princesses by a wide margin.
Merida still refused to so much as court anyone, much less marry them. Mulan II proves Mulan did not run off to marry her man after the first movie. Rapunzel had to rescue Flynn and only saved his life through a plot armor Deus ex Machina after he sacrificed himself to help free her from Mother Gothel (whom Rapunzel ended up killing herself). Tiana had accepted living life as a frog married her guy expecting them to both remain cursed after she changed him for the better. They still might choose to be with the one that shared their hardships and adventures, but Belle was the turning point from Damsel in Distress to independent character.
Mulan isn't a Princess movie. She's not a Princess and doesn't end up one through marriage at any point in the future. Belle doesn't start off a Princess, but ends up one eventually so she counts, Mulan does not. Li Shang is a military officer, and not royalty. She doesn't count any more than Wendy from Peter Pan or Alice from Alice in Wonderland does. None of those films are princess movies and they are their own separate category.
Sequels don't count because they retcon for story purposes. It's pretty obvious that Jasmine ended up married to Aladdin shortly after the end of the first film, but it was retconned to fit the plot of the sequels and television show later.
Modern Disney Princesses still end up married to someone they barely know. They end up being rescued, even Rapunzel was in the end. She doesn't kill the witch, he does when he cuts off her hair. You could argue it was Pascal, as he tripped her and sent her through the window. They know a guy for a couple of weeks at best, have an adventure with them, end up being rescued, and decide that they are their true love.
Brave is also Pixar, and that's a different issue. Pixar movies aren't really traditional Princess movies. Yes, she's a princess, and yes Disney owns Pixar, but they are a separate studio from Disney proper, that does the Princess movies. She counts as a Disney Princess, but not really as one of the Disney produced Princess films that use traditional fairy tales. Brave is an original story that is not based on any existing traditional fairytale.