In answer to your question, ask the dentist why the teeth need to be crowned. If it is preventing a broken tooth or cosmetic, you might skip the crowns. However, if your mother is at risk of infection or tooth loss, I would suggest you do something.
Analyze the situation the same way you would if your 90 year old mother needed a hip replacement. Is she young at heart? Does she swim and play golf every day? Get her the hip and allow her to keep enjoying her life. Is your mom bedridden in a nursing home? The hip won’t improve her quality of life and the surgery might actually kill her.