Mom tells me things about her assisted living facility. How do I check to see what's true & not true when I can't get in because COVID?

Unfortunately you will have to choose who to believe, your mother who you know is not a good reporter of the truth or the nurses at the facility.

It is very hard, when you cannot go check due to Covid.

You have excellent stories there to prove that Mom is not in her right mind where the things she sees as real are concerned. It is easy for you to discern that these things never happened when the shooting and the ducks occur. But more difficult when things that actually COULD be happening are concerned. You have seen her now as an unreliable story teller, and that she likely is. There is no way for you to comb through and understand what is real and what is not. I have had this experience. "There was a bird in the room; Al couldn't catch it for me". Spoke to Al. No bird. "There are drones over the hospital bed spying on me". Trace that down and there actually ARE these things attached to the ceiling to read heart monitors, with little foursomes of antenna coming out. Could look like drones but aren't. So quite honestly, there IS no way for you to know for certain. You will have to trust the staff, esp. knowing that your Mom is not seeing things right now. You have no choice. What a dilemma, huh?