Henrietta is aware that her elderly client, Omar, has had his driver's license revoked due to several minor accidents. She notices, however, that Omar drives himself to his therapy session. She shares her concern with him, and Omar leaves the session in an agitated state and does not return. In reading the case study, do you believe the therapist has a duty to notify the authorities? Why or why not? If she discloses the information, could this be considered a breach of confidentiality?

This is an interesting question. Theoretically, Henrietta should have provided Omar with a document when he first engaged her as a therapist, in which she should have outlined her privacy policies and explained when the confidentiality between a therapist and a client falls secondary to the therapist's obligations to disclose. Has this been done? If it has, then the situation is slightly different—Omar will know that his therapist is obliged to breach confidentiality if she feels the client could be putting either himself or other people in immediate danger. In this case, we could argue that given Omar's history of causing accidents, his continuing to drive is putting other people in danger.
However, the question then becomes: is the danger really immediate? The timeline is important here. A therapist is not allowed to breach confidentiality simply because she knows her client to be breaking the law, as Omar is doing here, unless there is an immediate danger perceived to either client or the general public.
In favor of the therapist breaching confidentiality, we could point to the fact that Omar has left the office, presumably in his illegally-driven car, in an "agitated state." He is an elderly man, he is agitated, and he has a history of causing accidents. He should not be driving. The therapist could argue that she perceived the danger to the general public and to Omar himself to be immediate here because of his state of mind.
Alternatively, we could argue that, having warned Omar of what she knows, the therapist has done all she is legally allowed to do unless the state or federal government asks her to reveal information using a court order. But the agitated state seems to move the issue from one of legal concern (Omar is breaking the law) to one of immediate physical concern for the health of the patient and the general public.
I would argue that the therapist could wait and see if Omar continues to drive after his warning, but also she would be able to argue fairly that his mental state, combined with other factors, upon leaving her office meant she could disclose the information or call the police with impunity. Moreover—how did Henrietta come by her knowledge of Omar's driving ban? This is also a pertinent part of the equation. Was this something told to her in confidence as part of therapy, or does she simply know about it as a neighbor or family member might?