If you feel embarrassed by her superficial appearance, why don't you do like Cher Horowitz did in "Clueless" and give her a makeover? (be nice and gracious about it). Maybe your sorority could even have a self-image and "putting your best foot forward" night or something, dedicated to personal development for ALL the sorority members.

Try to get to know this person on the inside, and remember that she laughs, cries and feel pain just as you do. At the same time, reach out to her. I noticed that you said she has a mustache...maybe some of the pledges could go to a spa together for some "girly bonding" and beauty treatments...one of the estheticians might discretely suggest a wax for her upper lip. Then hair style, eyeglasses...all those things can be very easily changed.