Advice needed

Hi 👋🏼 non really parent related as such but I don't know where else to ask for advice. My husband is a manager. He manages two other people in his office. One of the girls is new, she acts very immature and goes through bouts of not speaking for days and blanks people when they try and talk to her. She is very rude and immature. She has also started saying bitchy things to the other girl to her face which is unprofessional and not on. Anyways my husband has went to the main boss and said about her behaviour (to which nothing has been done) and has also said to the girl do you need any help or is there anything he can do. she said no. Problem is the atmosphere in the office is turning frosty and the silence is deafening so to speak. Anybody any advice on what he can do. It is starting to affect his well being and mental health in work.