the one motherly girl amongst the group who can still take care of friends (hold hair while friend throws up, walk friend to the restroom to piss, make drinks, carry/walk friend, etc.) while being drunk herself and not being bothered by it at all.
Girl: I really hope I don't get drunk and stupid at that party tonight.
Boy: Don't worry Diana is gonna be there. She usually enjoys playing the role of Mother Grey Goose when we're out at parties.