Final answer:
A parent can gauge toilet training readiness by observing if their 2-year-old daughter can recognize bladder fullness, as this is a crucial developmental milestone for successful toilet training.
Step-by-step explanation:
When a parent inquires about toilet training readiness for her 2-year-old daughter during a visit to the pediatrician's office, a key factor to look for is when the child can recognize bladder fullness. This ability to recognize bladder fullness indicates that the child is starting to become aware of her body's signals, which is essential for successful toilet training. While other factors also contribute to readiness, such as the ability to hold urine for several hours and control urination until seated on the toilet, the recognition of bladder fullness is an important developmental milestone indicating that a child may be ready to begin toilet training.