The only thing that I have heard of is that new carpeting and wall paneling can off gas.. I think these they off gas for a period of time. Some people are sensitive to it. I have not noticed this at all. It's probably worse when stored all closed up in hot weather. But open a few windows...get a cross breeze going...turn down the temp on the a/c...I don't think it's a problem,
Manufacturers are careful about venting batteries...and all come with smoke detectors, carbon monoxide detectors, and lp gas detectors. They are interested in your safety. Our lp gas detectors picks up dog farts..,since our male Samoyed likes to sleep near the detector. It's woken us a few times in the middle of the night.
The biggest hazards that I can think of is parking too close to rising rivers, parking under dead trees, and the occasional dometic fridge fire.
You might buy a used model that's off gased the new building materials...or rent a camper and have her do bloodwork before and after camping to check IGE levels...see if she has an immune/allergic response to the camper.
I would worry more about radon in a home than anything in a camper. Most campers probably spend more time outdoors and are healthier for it.