If guys hit on her but don't go out with her, then be different.
ASK HER ON A DATE.
It's quite simple. Be different. If she's attracted, you'll know. When you're alone with her, make a funny remark, or start to talk to her a bit and then leave. Don't be like the other guys who will stick to the last dying second talking to her in hopes of getting with her. Be a man who knows what he wants and knows how to take it.
So this is what you do. You go up and talk to her, you make a little comment, you have a short conversation. Leave on a high note that will keep her interested in you and leave. Keep her curious as to why you aren't like other guys. She knows the other guys like her, but she isn't quite sure with you. She wants to know what you think and what you want. She has to be INTERESTED in you.
So the time you talk to her after that, have a nice short conversation. Say you have to go and tell her to jot down her number. Call her up and say you're free sometime and you two should get together for coffee. Take her out on a date.
Don't treat her like some goddess that every man wants. Treat her like a bratty little sister. Joke with her, keep her laughing, don't give away your intentions, make her wonder. Leave on a high note once again and if all things go well, you can call back later on and ask for the date.
For girls who get hit on often, you NEED to be different. You need to attract, not pursue. She needs to WANT you and PURSUE you. That is what women crave.