That's Ari - Increase your sanity to keep her from attacking you when she pokes her head in the room to check on you, the other girls cant enter the room while shes there, so just grab the plush and squeeze it rapidfire 4 or 5 times. (Wouldnt recommend more than that cause the shark will come eat your face.) Don't let your sanity get too low while shes eyeing you until she leaves the room.
Theres a plaque on the inside of the office that tipped me off on how she works: it has her face on it and underneath the text reads "Champion of Mental Health" .... That was our clue. Until I figured that out I was stuck on level 5 as well.