I understand not being told the truth right away feels annoying.

But what does it matter to you who visits the office? You don't need to know things like that if the people don't appear in the middle of your session interrupting it. We are not supposed to know that much about other people in therapist's office. It is a very private place for obvious reasons. They might be clients or other people that have right for privacy, like family members who have some important business there. Maybe instead of stumbling she should have just told you that she can't tell you this for privacy reasons? Do you think it would have made you feel better?