I had Maple, Ayneris and Zoe assigned as Headgirl at different times with maximum charm, and "patronage" is my setting in every save, yet it doesn't seem to affect anything. I've always assumed patronage is used for lowering fear and stress faster... probably. But I haven't noticed any difference in frequency of quarrels as occurence with or without a Headgirl, it seems to be entirely random for "neutral" (as to who will be arguing with whom) and a bit more often for pairs with "aloof" relationship and worse. I check by reloading - slaves who don't have an opinion ebout each other vary, but those who already dislike one another usually keep quarelling between loads.
But that situation with my favourites hating each other is most frustrating and I'd rather not have them getting "Fickle" trait, so sex as a mediator is not an option(