Can a church be haunted?
Psychic and Paranormal
My Mom is a retired pastor. She has some psychic abilities. But she blocks it because it conflicts with her religious beliefs. And she struggles with talking to me about ghosts or my own empathy. So I know how that is. She's not changing any time soon (religions really close off the mind). I'm sure your Pastor is not going to want to believe this either. Plus, even if he did, he doesn't want that type of story to get out. People go to church to feel safe and worship. What does that say about the church that a demon or strong entity resides there? Trust me, he won't want to deal with that.
If you can, order that book I referenced. It's perfect for your situation. Entities like dark, quiet areas. But they are especially drawn to areas that are cluttered, have low energy, and have some decay (like a lot of trash around). You made it sound like that lady's office is a cluttered mess so that totally makes sense.
The book I referenced goes into how overshadowing and possession happens. And it's not that easy for this to happen to anyone. Although children are at higher risk. So you should not be overly afraid. The book also talks about many tests the author has done with regard to running water in hoses and pipes. Running water with pipes anywhere (below or above ground) are a barrier most entities are unable to cross. And because of this many entities get trapped in buildings and are boxed in a range where water pipes flow. This is also why you wash your hands when you are anxious to feel better (any negative energy or entities will temporarily jump off you when you expose yourself to running water). This is also why anyone with psychic abilities feels better when taking a long shower.
So the question you have is what to do? If you illuminate the area with sun light or bright lights, you'll just chase it away to any other dark areas of the building. So I'm not sure that accomplishes much. You need to know that their power grows as the night gets long (strongest just before dawn). Keep that in mind while doing tests. You could try to smudge the room at night while also doing your clearing exercises. But then it leaves a strong odor that you're going to have to explain the next day (a lot of people think smudge smoke smells like pot).
Has the entity come at you with a psychic attack yet? That's where you instantly feel sick and weakened and have sharp pains as if someone is knifing you? And does this entity seem to always keep to that room or do you feel it in other areas as well?