Poor mommy, poor daughter. Be sure your vaporizer is clean. Mold and mildew can build up in some designs, and that can create a whole new layer of allergy and illness. Be sure her room, especially around her bed, is dust-free, and that could include running stuffed toys through a cool dryer cycle to help remove deep dust. Wash all bedding and jammies in a scent-free detergent, and put a cup of vinegar for softening and extra cleaning in the rinse cycle. Avoid dryer sheets altogether – they contain seriously toxic ingredients, and can trigger lung and other irritations (I get asthma when I get a hit of somebody's fabric softener).
You might also find a naturopath can do wonders for her underlying problem. I've heard that chiro treatments can help, but it sounds like you need something more.
Finally, you'll probably get many recommendations for Vicks on feet or chest. This apparently does help some children, but use with great caution. There's at least one recent study showing that Vicks and other mentholated compounds actually increase congestion for many kids. If you use it, watch carefully for her response.
I sure do wish you both the best. I've had chronic lung problems my whole life, and have lost plenty of sleep over it.