I had a similar problem about a year ago, when lying down or standing up. Dizziness and nausea sometimes. My Dr. also said it was age-related, and explained that it is 'bits' moving about in the inner ear and touching I can't remember what. He prescribed things.

Coincidentally, I was working for an elderly and very smart lady, who said "Oh I get that. I've found if I bang myself on the head, it goes away," and she demonstrated by smacking her forehead with the heel of her hand.

I tried it, and it DOES work, for me too. Instantly. I refined it to a sharp shake of the head, which engenders less spousal amusement because it is less noticable.
The problem went away for me, as the quack said it probably would.

Gnu, this 'Mrs. Bell's Manoeuver' HAS to be worth a try, cost and drug and pain free as it is. Good luck to your mum.