HELP! my gran is a very dangerous driver!?

My gran is in her mid 70's and is an awful driver. There is no way she would legally pass now, she stalls in the worst of places, crosses over lanes on a roundabout without indicating or looking around, has no lane discipline whatsoever, drives everywhere in first gear and drives around with her indicator on then turns the opposite direction because "she can't hear her indicators clicking". When we try to speak to her about it she refuses to listen or retake her test but this has got to stop. She aknowledges the fact she drives eratically but thinks this is different from being dangerous! I beg to differ, I've been in the car before when she has been breathalised by police for her dangerous driving! Please help before she kills herself or someone else! Is there any way she can be made to retake a test?