This girl has exercise induced asthma. It is not well understood why it happens but the triggers are recognized. Normally when breathing occurs air is taken in by the nose and the nasal passages and turbinates act to remove dust and humidify/warm the air. Logically this makes the air denser Pv=nRT. So when exercising, breathing through the nose is decreased and replaced by more vigorous mouth breathing. This means the air is not humidified and warmed up. The air is less dense and the asthma ensues. The question took this same principle except reversed it by asking what external condition could lead to the asthma and that would be cold dry air.