I remember when I was small, I used to smell air from a negative ion (fuuu ley jeeee) machine. That makes me breath better, see if you can find those machines.
if your daughter only caugh at nights. There are things you need to check first.
1. The cleaningness of air cond. filter . Wash it at least every week.
2. Any unnecessary dolls placed at her bed, pls remove them.
3. Wear scarf (a thin one) when she goes to bed.