If my chapter had had parties that were, ahem, against national policy (like mixers), we would have paired up with a fraternity and held the "ice cream social"
off-campus at a member's house. The only people invited would be members from my chapter and the fraternity involved, and possibly boyfriends/girlfriends of members (but not usually, since that tends to create drama). Of course, there would always be designated drivers present--
if my chapter had had parties like this, we would've called our Sober Sis.