Mom had a stroke, does she have dementia? How much do I need to do?

My mom, 90, had a stroke July 1. I spent most of July, Aug and some of Sept with her during rehab. Even with rehab, continued to decline. Became paranoid, suspicious at second rehab facility; dxed with vascular dementia. Moved her to AL, she passed out there; in hosp with extremely high bp for 5 days, back to AL in demntia unit with 24/7 aide. Fell, broke her hip, surgery. Now again in rehab. We think, because she's now in a Catholic place with lots of priests, nuns, stained glass, much calmer, seems to be progressing. Walking with walker. No longer thinking that she owes money; no longer saying that she's a bad person, not worthy of prayer. Is this dementia? How do we tell? I really, REALLY don't want to put her through another MRI, she wept through the last one. Her last CAT can, two weeks ago, when she broke her hip, looks like her brain is swiss cheese, to quote the doc who read it. She is now having sudden onset headaches, across her forehead every afternoon. Take her to a neurologist? To what end? Just feeling at sea here; my brother, who is POA is ten minutes away, but we are all HCPs and I am a psychologist with a limited amount of clinical knowledge.