She is very pretty but doesn't get asked out by guys? Please answer!?

My friend is a very beautiful (confirmed by most people at school), easygoing and fashionable girl but she is upset that she has never been picked up by guys (ie on the street, library, etc.). Her other girlfriends, who are not as pretty got picked up. Is it true that guys don't ask really beautiful girls out at first sight? What can she do to "improve" her guy-luck?