As assistant directors, we forget that it is our job to be a part of the team and support each other. I've been in similar situations. I would recommend that you mention the importance of being a team. Those of us that are fortunate to teach in a team teaching situation, often forget that it is a privilege. I do not know the current dynamic of your team but our team openly discusses everything. We even discuss the things we disagree about. It helps us ensure that we are providing the students with every opportunity to succeed. In my experience, a good team will compliment each others strengths and weaknesses. They will also have healthy discussions about teaching styles, decisions being made & anything else you can think of. Take some time to have these discussions with this person about being a good team member. Also, encourage team discussions about new ideas and teaching styles. It is possible to help lead a team, even if you are an assistant director. This individual really sounds like they need a mentor to quietly and patiently steer them in the right direction.
Just my 2 cents.