My chapter of Sigma Kappa has heart sisters, pearl sisters and big/little sisters. On bid day each girl gets a heart sister (like a pre-big sister person) and a pearl sister (but this is kept secret until whenever the pearl sis feels like revealing herself- which in some cases was years later if ever
) and then half way through pledging the girls mutually select big/little pairs.
Sometimes girls have unofficial adopted big/little sisters. Me for example. My big sister stopped talking to me once she found out I was friends with a sister she was fighting with. Officially she is still my big, but I was adopted by the girl she didn't like. I think its sad when things happen that way, but sometimes you can't avoid it I guess.