How to help delusional Mom?

I appreciate all your responses, but in this situation, my mom isn't just angry - she's angry with ME, for something she thinks I actually did - not because I didn't believe some random other delusion.  Dogs are allowed in this facility - my niece actually brought her dog to visit before Christmas, and this may have triggered the delusion, which was then probably exacerbated by her hearing a dog barking down the hall (according to an aide).  She has had other delusions that I do go along with, but I don't want to lose her trust or have her believe that I would do anything to harm or upset her - I'm really afraid that if I "fess up", that's going to really backfire later when she hears or sees another dog and thinks I've been lying to her about lying...and so on.

Actually, writing this has given me an idea - we could tell Mom that the dog is my niece's dog, and she realized where she left him and came and got him.  Maybe that would work, at least for now.  Thanks again, I do appreciate the helpful suggestions.

Usually it is better to go along with the delusion and not tell the person it is not true. My mother told me someone stole her favourite nightie. Later she told me they returned it and what's more they had mended it. She was delighted, but would have been angry at me if I told her it was not stolen. I just said, "That's nice."

I agree with Ahmijoy and your husband. Apologize and tell her you will take the dog with you. Her delusions are real to her. Part of the Dementia. Can't change it.

Oh, dear, Rosemary. I totally understand what you’re going through. 99.9% of my mother’s symptoms of dementia were hallucinations and delusions. The worst was a “young boy” who “rode a bike” up and down the “road” outside her “apartment”. He was stalking her and stealing her dirty underwear. In fact, it was a old man in a wheelchair and he was not “stalking” her. Plus, the laundry aides were the ones who were “stealing” her underwear (to wash them).

One day, Mom was on an angry rant about this “young boy”. The aide who was assigned to her heard her and me trying to placate her. She casually walked into Mom’s room and just as casually joined in the conversation. She actually told my mom, “Oh, Miss Joann, didn’t you hear? He got fired. He isn’t allowed to ever come back into the building!” My mother believed her and she never mentioned the “young boy” again. Maybe you could ask an aide to do the same for you. Have them tell Mom that dogs are not allowed and they spoke to you and told you to never bring the dog in again! Of course, you promised you wouldn’t. Maybe it will work for you. Sometimes the word of a “stranger” carries more weight with them than that of a relative does.