That is a good observation on your part. Wheezing is not normal. True wheezing originates in the lungs but similar sounds can originate in the larynx (voice box) or the throat. Once a year croup is not uncommon and is not necessarily a sign of underlying lung disease, even though premature infants are more inclined to have lung disease than full term babies.
You would do well to have your daughter examined by her doctor who should be able to determine location and cause of the wheezing and treat it accordingly. You should also pose your question regarding recurrent croup to her doctor.