Do you consider Mulan to be a Disney Princess film?

Her parents aren't royalty and she didn't marry into royalty, so she isn't a princess!!

but she can be

I don't. I think Disney includes her as one to try to make themselves seem more racially diverse in the princess category. She is a heroine (and an awesome one at that), but is in no way a princess.

She is an official Disney Princess look at the official Disney Princess website

She's part of the Disney Princess franchise, but she is not an actual princess. Going by the definition of a princess ("a daughter/granddaughter of a king or queen or the consort of a prince") she isn't one.
While she is part of the princess franchise this question was is her movie a princess movie, and since it at no point features a princess then in my opinion there is no way it can be a princess movie.

She's a wonderful character (one of my favourites) but as I've said before Princess is a word that has an actual meaning, it isn't just a compliment it's a title, and being a cool or heroic character doesn't make you a princess, being royalty or marrying into royalty does.

I'm fine with her being included on the spot seeing as so many people feel strongly about her being a princess, but going by the definition of the word princess Mulan is not a princess. Besides, she's a hero and that's arguably a better thing to be, so I don't know why so many people would rather have her title be princess when really it's hero :)

she's a heroine, not a princess

if she's a princess, why not?

she could be but she is not

There is no reason she should be!