I think where the confusion lies is that even though little sister groups are pretty much outlawed today, they do still exist "unofficially" on many campuses.
I think these are the names that OP was looking for.
I can't remember what the KA little sisters were called on my campus, but as carebearwcu mentioned, they did have their KA Rose who was the "head" little sister.
Granted, people who are not in that GLO (and, a few of the brothers in that GLO), will still sometimes refer to these little sister groups as frat rats, house whores, XYZ whores, etc., when this is not necessarily true of all of these women (sure, there are some).
I think roqueemae's comment was totally uncalled for.
Edited for further clarification:
Not all little sisters were frat rats, and not all frat rats were little sisters. Sometimes the members of the little sister groups would make fun of the girls that hung out w/ the fraternity but weren't little sisters...and call them house whores.
Most of the time the "Rose" or "Sweetheart" (head little sister) WAS a little sister -- she was just the one that was chosen to be included in the composite since she received the honor.
Another difference is these little sister groups could wear letters, put the fraternity's sticker on their car, etc., whereas a plain old frat rat cannot.
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