Sophie1982,
You seem like a self-assured, positive young woman. Let those qualities, plus your intelligence and attractiveness be your ticket through rush!
If potential future sisters are more concerned about your appearance representing the sisterhood, versus your actions and deeds, then perhaps they aren't worth it. Look for sisterhood where it truly is, rather than where it appears to be.
I certainly don't fit the "image" of the average greek woman on campus, and I sensed that this would not be acceptable to many of the houses on campus. (I have priorities that do not include being perfectly made up at all times - I understand that is important to some, but it's not to me.) So I didn't go that route. I am now happily involved with my own sisterhood, where I feel comfortable with myself and my sisters.
Best of luck to you!