I guess the slut outfit should count, but I don't think there's a specific path where she becomes a total nympho besides some endings (e.g., the camgirl ending where she invites a viewer and practically becomes a sex slave)
does the achievement overview say that you have 8 endings unlocked? and does the replay gallery say you need 8 endings unlocked?
might require having luxury items and progression with the other AV shooting scenes. I tried to unlock the Drink It AV shooting with a new save from scratch but I can't really figure out what the specific requirements are. maybe someone else knows?