Final answer:
A drop-off appointment is the best option for pet owners who do not wish to witness their pet's euthanasia, providing a way to say goodbye before the procedure without being present.
Step-by-step explanation:
If a client does not want to witness their pet's euthanasia, a suitable option would be a drop-off appointment. This allows the pet owner to say their goodbyes at their own pace and leave before the actual procedure. The veterinary team then carries out the euthanasia with compassion and professionalism in the absence of the pet owner. Options such as virtual appointments, extended appointments, or group appointments do not typically apply to pet euthanasia as they either do not remove the owner from the immediate situation or are inappropriate for the sensitive and private nature of the event.