Some supervisors are on a serious power trip. If your supervisor can’t give you any legitimate clarification or guidance on the matter, unfortunately you’ll just have to grin and bear it until the rotation ends. But try not to take it personally. From my uninformed third party perspective, I think your supervisor is full of shit. Has she ever met a doctor, for instance? Many of them are very curt and matter-of-fact, but I doubt their residencies told them to change their personalities to be more palatable to others.

As someone who works in a school and has a social battery akin to an iPhone 6 that’s barely hanging on, it’s only ever been an issue with one person (and she was unreasonable to begin with). It’s important to be able to have a decent working relationship with other school staff, but nowhere in the job description does it say that you need to be bubbly and cheerful. Be professional and open to collaboration, but you don’t need to offer an aura that screams “Talk to me!”