Looks definitely mattered in my chapter, however at the same time you could've been the prettiest girl on campus but if you didn't have good grades and you weren't involved in high school, you had no chance. We wanted girls that could keep us going not just in the social arena but academically and otherwise.
And let me just say, people tend to look much better when they're showered and put together. I was always taught never to leave the house without spending some time on my appearance(unless, of course, it's an emergency).
In general, you definitely do not have to be drop dead gorgeous to be in a sorority. Just dress nice and please shower beforehand!
And remember: the most important thing you wear is your attitude!