My friend got me thinking

Ok, so today i had classes but when i went to class my teacher couldn't come. My friend (who goes to class with me) decided to go and drink some beers. Then we decided to pick up one of our friend who lives on the way to the bar. He wasn't home, but his sister was; who asked me what my name was (note - this was not the first time she saw me). Then i introduced myself and what not (btw we're both the same age). Then we left for the bar, but my friend who was with me (my friend who goes to class with me) told me that, our friend (the one we stopped to pick up, who wasn't home) sister graduation ball is coming up (next week or something) that i should ask her if she want's me to go with her. The few times i've seen our friends sister, she doesn't really attract me; that much, but at the same time i don't really dislike anything about her. Maybe it could be that i'm slightly drunk right now but i don't know what got me thinking about this girl so much. Should i really ask her to go her graduation ball with her or should i just chill the fuck out. I somewhat know what i should do, i'm pretty good at making relationship decisions but i want to know what the temp has to say.