Final answer:
The priority nursing action for a postpartum client with cystitis is to encourage increased fluid intake, which helps reduce bacteria in the urinary tract and supports recovery.
Step-by-step explanation:
The nurse's priority nursing action in the care of a postpartum client diagnosed with cystitis should be encouraging increased fluid intake. Increased fluid intake can help flush bacteria from the urinary tract, dilute the urine, and facilitate recovery. While administering antibiotics is an important part of the treatment plan for cystitis, this is usually done based on a physician's prescription after sensitivity testing, not as a prophylactic measure. Providing sitz baths and instructing the client to limit ambulation can be supportive strategies but are not the priority actions. It is important to note that antibiotic use must be carefully managed to avoid complications such as C. difficile infections or the development of antibiotic-resistant infections.