How can I tell my mother she can no longer drive?

I am planning to tell my mother who has been recently diagnosed with Alzheimer's that she can no longer drive. Her neurologist has shown me significant brain lesions in her memory center on the MRI. Before the doctor takes her license away, or before an accident, I want to take the responsibility - and avoid any injuries to my mom or others, or hurt feelings by having my mom told by a stranger. i am dreading this. I actually am taking ulcer medication. My sibling does not live in the same country. Please help me with the dialogue... I know I will have to walk away with her car keys.