A 3-year-old girl presenting with a barking cough and inspiratory stridor most likely has which diagnosis?

The presentation of a barking cough and inspiratory stridor in a 3-year-old girl is most consistent with croup, which is also known as laryngotracheobronchitis. Croup is characterized by inflammation of the upper airways, leading to the distinctive cough that resembles a seal barking and the stridor that occurs when the child is breathing in. Typically, croup arises following a viral infection, and its symptoms often include a preceding upper respiratory illness.

In contrast, bronchiolitis is more commonly seen in infants and is characterized by wheezing and difficulty breathing due to inflammation of the bronchioles. Pneumonia usually presents with fever, cough, and potentially consolidative findings on exam or imaging, rather than the barky cough and stridor associated with croup. Foreign body aspiration can also present with stridor, but it typically involves acute onset and is often accompanied by choking or respiratory distress, rather than the gradual development that is typical in croup.

Thus, given the specific symptoms of barky cough and stridor, the diagnosis of croup is the most appropriate choice for this case.