Final answer:
Reminding the client to move her head from side to side to increase her visual field is the most appropriate nursing action for a patient with homonymous hemianopsia following a left-sided stroke.
Step-by-step explanation:
The most appropriate action for a nurse to take for a client who had a left-sided stroke with homonymous hemianopsia is D. Remind the client to move her head from side to side to increase her visual field. Homonymous hemianopsia is a condition where there is loss of half of the field of vision on the same side in both eyes. This action will help compensate for the lost visual field and improve the patient's ability to see potential hazards, thus reducing the risk of injury. The other options, such as assessing for bladder and bowel retention, listening to lungs after eating, and supporting the patient's left side, may also be relevant in overall stroke patient care, but they are not directly related to managing homonymous hemianopsia.