Final answer:
The nurse's priority action is to report signs and symptoms of obstruction to the physician.
Step-by-step explanation:
The nurse's priority action in this situation is B. Report signs and symptoms of obstruction to the physician. A newly created ileostomy should be producing output within a few hours after creation. The absence of ostomy output for 12 hours, combined with the patient's worsening nausea, suggests a possible obstruction, which requires immediate medical attention. The nurse should notify the physician so that appropriate interventions can be initiated, such as imaging studies or surgical intervention if necessary.