Well, I may not be a parent yet... But I understand your kid. Coz, I am also practically almost a teenager. I am 22. And I had been almost a tomboy always. Not too pretty or anything...
And I have always got along well with boys. They thinks of me as one of them, and never even bother to notice that I am a girl.
I almost got a crush on one of my boy best friends, and then noticed that he doesn't even notice me as a girl. So, I gave up...
That is sad, sort of...
Well, then, my best friend, a girl, though she is tomboyish, she has always had a steady boyfriend for the past 6 years.
My sister who had a bf for the past 4 years is getting married now, some other girl friends have got engaged as well, and all the male friends have got girl friends, or love interests or crush or things like that too...
You tend to feel lonely you know, when everyone around you has 'someone special', and you have just your friends and family...
I have always thought, if I were a bit more girlie, or prettier, will they have looked at me???
Then I feel I shouldn't change myself.
Teenage, is a much more complicated stage. You don't much about life, and you tend to feel more sad coz guys doesn't notice you.
Have you considered that your daughter might have a crush on a boy, and he is not even noticing her or something? It can happen, and it can hurt a 15 year old like hell. She might be going through a bad stage of her life. Must be sad... I feel empathy for the poor kid already. :-(
But unfortunately, I cant think of a solution. She shouldn't change herself for being liked by a guy. Coz I think, if a guy should like a girl, it will be honest only if he likes her for who she is. Tell that to your daughter ok. That she shouldn't change herself, and one day...someone will like her for who she is. And anyway, she has the whole life ahead of her. She is just 15.
And if it helps, tell her my story. 22 years old, and never been asked out.
(Don't know if this helped...)