Should I Ask Her Out On A Date?

In short, I think that this might be taboo because I am a Senior and she is a Freshman, but I like this girl. We never really talk, but we smile at each other a bit. The thing is, one of her best friends, and one of my best friends are dating. My friend is trying to set me up with one of his girlfriend's friends, but not the one that I like. He wants me to double date with him and his girlfriend. Should I ask out the girl I like instead of the other girl. She seems really sweet, and I would like to get to know her a little better. I think that she likes me, but it seems like she likes this other guy as well. If I don't make my move it will be too late. I'm popular at school and everything, and I'm a Senior opposed to the other guy who is a freshman, but I'm afraid that if I approach this the wrong way that I might overwhelm her. What should I do here?