One sided sexual attraction is possible on the girl's part as well. However girls and guys should realize that doing stuff like asking their friend out is annoying to say the least and should be avoided. It's perfectly normal to have a friendgirl and you don't have to have sex with someone just because you're close to them and they are the opposite sex.
John: I'm just hanging out with Sarah tomorrow.
Bryan: You're a major pimp Sarah's hella fine.
John: Dude she just my friendgirl.
me: oh she's not my girlfriend yet...for now she's just my friend girl