Why would our dog suddenly avoid my mother (96)?

Another thought, 'rather sit outside in the rain'.
Dogs want to be left alone, often, when they themselves are sick.

My dog was 14 1/2, and getting disabled neurologically. She started to cling towards me more, and avoid my husband, as he did not know when she could no longer walk or how long she could go out for-I am guessing. She was older though. She avoided him because she herself was ill.
Be sure at any age the dog is well by having it checked up by the vet.
Arrange supervised visits with the dog and Mom.

Well, there is a cat named Oscar who keeps a quiet death vigil at a Providence nursing home. On the other hand, a schnauzer named Scamp, in Canton OH, becomes alert, paces and barks to call the nurses when a patient is dying.

That is what i think too. Have heard about animals who sense illness and changes in people and think that this is an example. AMAZING!

The dog knows something is wrong. She senses something.

My little 5 # Chihuahua acts very funny around my 86 year old FIL. She has these funny little rituals, like every night, whe he goes to bed, the dog knows that the Old Man will scrub his dentures, go to the toilet, and when he comes out, she yaps at his feet, barking. Every night! Also, in the middle of the night, she does patrol, to see that everyone is in their beds snoring away, and does her business, and then returns to bed. Dogs have pack mentality, and if she is not a member of the original pack, then she may never ve accepted, as she may not have ever been given the kind of love from Mom, at an early age.

Jacksam, dogs have a high sense of hearing and smell, maybe there is something that is making the dog very uncomfortable.

What are your Mother medical issues? Did your Mom recently moved in, and the dog could be jealous? Any new medication that your Mom is taking that the dog doesn't like the side effects that only the dog can sense?

Pam had a good idea, maybe your Mother accidentally tipped on the dog or stepped on her, so the dog feels she doesn't want your Mom to get hurt so she stays out of her way.

Set up a nanny cam. Maybe grandma rocked on her tail or accidentally stepped on her.