Final answer:
The next best step in the management of this patient with tension, depressed mood, and decreased productivity towards the end of each cycle is to ascertain the timing of her symptoms each month.
Step-by-step explanation:
The next best step in the management of this patient would be D. Ascertain the timing of her symptoms each month. The patient is experiencing tension, depressed mood, and decreased productivity towards the end of each cycle, suggesting that her symptoms may be related to premenstrual dysphoric disorder (PMDD). Ascertain the timing of her symptoms each month will help confirm the diagnosis and guide further management.