I agree, google some bid day pics from throughout the South and you will see girls of all sizes and looks among the actives and new members. It is a myth that they are all slender and gorgeous, although obviously, many are.
What they do all seem to have in common is a sense of style, grooming and confidence. Cultivate your outer beauty --everyone has fabulous attributes--and cultivate your interior life. Be happy with yourself and it will show.
Also, the number on the tag isn't what you should get hung up on. A 5'1" size 16 is vastly different than a 5'11" size 16.
With what everyone has said about getting clothes that fit you no matter your size, everyone is going to have certain stores/manufacturers that don't work for them no matter how hard they try. Avoid these, they'll do nothing but bum you out.
__________________
It is all 33girl's fault. ~DrPhil
Every girl going through rush is nervous about something, whether it is their appearance, not knowing anyone, an iffy GPA ,etc. The best thing you can do is put your best foot forward and try to convey a confident (but NOT arrogant) demeanor.
Read up on each national organization and on the local chapter's history. Practice rush conversation with someone- even over the phone.
Hybrid Mode
