Final answer:
The nurse should tell the mother to count the number of wet diapers her baby has each day and monitor the baby's weight gain at each pediatrician visit to ensure the baby is receiving enough to eat.
Step-by-step explanation:
The nurse should tell the mother to count the number of wet diapers her baby has each day, as this can be a good indication of whether the baby is receiving enough to eat. A well-hydrated baby should have at least 6 to 8 wet diapers per day. Additionally, monitoring the baby's weight gain at each pediatrician visit is important, as it can provide further reassurance that the baby is receiving enough nourishment.