I side with jespah let the doctor be the one to correct her.
Search for a geriatrist. They have a lot of hability and touch with elder patients. They now tricks about how to talk to them and make them behave.
As what happens with children there is always a way to make them understand their situation. Pediatrist do it all the time.
Many times an elder patients respects the indication of a doctor as a law, but discard any rules set by his or her kin.