The correct answer is 3.
Rationale: Based on her symptoms, S.M. is experiencing Grade 2 diarrhea which has not resolved despite antidiarrheal treatment. According to the Enterocolitis chart located at the end of the SCIMMUNE protocol, ipilimumab should be withheld until her symptoms resolve to Grade 1 or lower. She should also be assessed to rule out any infectious etiology, and may need to be started on immunosuppressive corticosteroid treatment with predniSONE 0.5 to 1 mg/kg/day PO if the problem persists beyond 3 to 5 days or recurs.