Final answer:
The nurse needs to closely monitor the postpartum woman for infection due to the manual extraction of the placenta, which can increase the risk of introducing bacteria into the uterine cavity.
Step-by-step explanation:
The factor in this postpartum woman's history that suggests a need for the nurse to closely monitor her for infection is B. placenta removed via manual extraction. After childbirth, the placenta should spontaneously separate from the uterine wall and be expelled. Occasionally, the placenta does not separate appropriately, which may necessitate manual extraction by the obstetrician. This process can introduce bacteria into the uterine cavity and increase the risk of postpartum infection. In contrast, a hemoglobin level of 11.5 mg/dL, a short labor duration, and multiparity are less direct risk factors for postpartum infection in this context.
Additionally, the postpartum period is a time during which the mother's body, including the uterus, undergoes involution to return to its pre-pregnancy state, facilitated by breastfeeding among other factors. The nurse must observe for signs of infection, which can include fever, foul-smelling lochia, and abdominal pain.