Charm #5: Needing you to accompany her
Because she is at or near her peak level of appeal to males, and because she cannot protect herself from the deluge of unwanted advances, she feels safe when you're there. You have to walk her back to her dorm, arrive first at the dining hall so she doesn't have to sit there alone while creeps leer at her, stare down these creeps once she does show up so that they leave her alone, socially castrate any loser guys who come near her to chat her up, and repel sales assistants at the mall who would otherwise lift her wallet.
(I know that arriving late, so that she gets nervous, is a common tactic to increase her attraction to you on a first date. I'm talking about once you've gotten to know each other.)
In addition to having to be there to protect her, you also need to accompany her in some cases because she is in a venue where being alone -- or at least, being without a boy -- marks her as an undesirable, which she will take to mean "ugly." When she is older, her male peers will have enough balls to approach women, so that attractive females will never be alone. When she is young, though, boys her age are nearly all too chicken to go up to her, so that many attractive girls are left alone, feeling that they must be repulsive to boys. See here, starting around 3:00, for how this feels:
At a young age, this is one of the worst feelings she can have, and as the night wears on and she becomes more convinced of her hideousness, she will deflate somewhere in the background. (Women my age can rewind to middle or high school dances when they stood alone, hopefully at least with their girl friends, while the DJ played Whitney Houston's "I Will Always Love You" or "It's So Hard to Say Goodbye to Yesterday" by Boyz II Men.) So when you ask her to dance, she is grateful to you for convincing her that her ugliness is all in her head, and will repay you by smiling and laughing bashfully the entire time, holding your hands or arms firmly, and gazing up into your eyes:
It's hard to underestimate the appeal of a girl who makes you feel like her protector -- it's not a need that can be even partly met by spending money, god knows, and there's nothing you can do in your relations with other men to fulfill it. And unlike sex -- another need that only females can help you out with -- the satisfaction is longer lasting. Any girl can fuck you, and a fair number can even fuck you very well, but something else has to fill in the gaps in between.
That's what some guys mean when they say, "You'll regret it if you don't date a smarty-pants," but there are other ways to fill this void. Boosting your sense of self-worth -- and yes, even getting that warm, revolting feeling when you take care of helpless things -- works just as well.
How to preserve this charm
Assuming you're over 25, you probably won't have to worry about guys approaching you, so just concentrate on conveying to him that he's your protector while you're dancing, strolling around, or whatever else. You still remember how to look up into someone's eyes and smile bashfully, don't you? And how to press yourself closer to him when you're walking outside, or rest your head on his shoulder? Of all the girly charms that can break through a man's defenses against commitment, this one is probably the easiest to maintain, or to fake when it's no longer there naturally.
You might also try what Method actors do, by recalling vividly a previous time when you felt the way you need to feel. Again, just rewind to those awkward middle and high school dances in your mind, play one of the songs that made you feel desperate for a boy to dance with, and this should put you in a more grateful state of mind before going out.