I had this problem of 'leagues' and such recently. I felt that some girl was 'out of my league', because I was pretty sure that she gets a lot of male attention and such. I resolved that if someone thinks they are out of someone else's league, then they don't deserve that person anyway. Thinking that you are too low for someone's league [which is what you say by saying she's out of your league' is just a way to lower your self-confidence and thus will lead you to inaction. And of course you'll think she's out of your league because she won't give you the light of day, which is because you think you won't get the light of day from her, and so you don't try! See what I mean? It's a vicious cycle. And you can stop it by thinking that people are not out of your league [and consequently, you are not out of other's leagues].
Just approach her like she is a normal girl. Don't let her intimidate you. Just talk to her... she is just another person. Once you become comfortable, then you can go from there.
If a dream comes true... then is it still a dream?