Final answer:
In case of magnesium toxicity indicated by a reduced respiratory rate of 6 breaths/minute, the correct action after discontinuing magnesium sulfate medication is to administer calcium gluconate to counteract the effects.
Step-by-step explanation:
A woman taking magnesium sulfate has a respiratory rate of 6 breaths/minute, which is a sign of magnesium toxicity. In this situation, after discontinuing the medication, the nurse should administer calcium gluconate. Calcium gluconate acts as an antagonist to magnesium and can help counteract the effects of magnesium toxicity. The other options, such as increasing the magnesium sulfate infusion rate, encouraging deep breathing exercises, or administering a sedative to decrease respiratory rate, are not appropriate and could be harmful in the context of magnesium toxicity.