My doctor thinks that my daughter is suffering from tracheomalacia. What does this mean?

Weakness of windpipe. Malacia is weakness of a portion of the airway (trachea is the first portion of the airway and bronchomalacia is weakness of airways further down in the lungs). It can occur when someone is born premature, after a bad infection or after a tracheostomy. Usually wheezing in the upper airway with shortness of breath is common. Breathing tests can help suggest it is present / other tests often need.
Usually nothing. Tracheomalacia is a problem that children usually outgrow. Unless they have had a repaired t-e fistula, or vascular ring, it rarely causes problems. Audible wheezing when breathing out (expiration) is the most common symptom. If the problem is noise with inhalation, the problem is not tracheomalacia. The best way to diagnose tracheomalacia is bronchoscopy.
Soft trachea. Softening of the trachea.The softening may allow the airway to collapse during expiration and perhaps mechanically interfere with the flow of air. Depending on how severe, surgery may be required. Your pneumologist will reffer her to a pediatric thoracic surgeon if she is 18y/o or younger if he considers it appropiate.
The wind pipe is sof. The trachea (wind pipe) is abnormaly soft and deforms upon breating or even remains collapsed most of the time. She should be evaluated by a thoracic surgeon.