As a medic I can offer some opinions that I believe to be valid.

1. A modestly priced inverter that plugs into your cigarette lighter outlet WILL easily power a nebulizer.

2. A nebulizer can be powered by an oxygen bottle. That is the way we do it in the ambulances. Put medication in your cup, hook up the hose and set the regulator to 6 to 8 cfm. A treatment takes about 10 minutes and a portable oxygen bottle will handle about 4 treatments. If your friend is seriously asthmatic she probably already has oxygen prescribed. If not, she should.

3. Those who counseled using ordinary shop grade compressed air are flirting with pneumonia at best, death at worst. Levels of lubricating oil, moisture and general rusty crud in shop air are dangerous. There is a reason that scuba tanks are filled with special compressors. Argue if you will but it changes nothing.

There is no reason you can't have a great time on your cross-country drive. Adult asthmatics seldom need a treatment on a regular basis, only when occasional cicumstances so require it. By all means have the ability to treat along on your trip but I'll bet that if you show her a good, stress-free time she may never need it.