I feel like this should go without saying, but apparently it needs reiterating: real people cannot be "manic pixie dreamgirls." It doesn't matter how "quirky" they are. It doesn't matter how cutesy they dress. It's impossible. And calling an actual human being a "manic pixie dream girl" is far more problematic than someone seemingly being one. Let's recap, shall we? The term "manic pixie dream girl" was invented by film critic Nathan Rabin to describe a common stock female character in movies. This female character is fun and adventurous, quirky, gorgeous, and completely, 100% dedicated to teaching the (usually awkward, usually angsty) male protagonist how exciting life can be. They'll ride motorbikes together and kiss in the rain. She'll have no needs or desires of her own. She certainly won't pursue anything for herself. She exists solely for the happiness and enlightenment of our boring hero, and if she doesn't bring him happiness, at least she brings him insight and a richer inner life.
It's a definition that literally cannot be applied to a real person. There is no human being on the planet who exists solely to provide quirky enlightenment to someone else. Of course, there are women who share certain traits with the standard Manic Pixie Dreamgirl. Women who eschew responsibility, women who wear frilly dresses, women who sing everywhere they go and like fictional worlds more than reality. But these traits are expressions of who they are, not of who other people need them to be. And if we accuse them of being a "manic pixie dream girl," we're basically stealing that self expression from them. We're accusing them of being fictional. Of putting on a persona to be more appealing to guys, of purposefully being "weird" and "quirky" for the benefit of men around them. It's another incarnation of the "fake geek girl," suggesting that any interests or personality traits outside the most basically, stereotypically feminine must be performed. They must be a lie.
And in doing so, we present a really constrictive idea of what a real woman is allowed to be. Originality is bad. Fun femininity is bad. Female awkwardness or intellectualism are unacceptable. Be less interesting. Be less noticeable. Be smaller. Because if you don't conform, you can no longer possibly be a real person. You're just a manic pixie dream girl, faking it to manipulate others, or else betraying your gender by perpetuating a harmful trope.
Which is precisely the attitude that criticisms of the Manic Pixie Dreamgirl trope are supposed to deconstruct.