A.V.
I would buy a reusable version that you can wash and dry in your regular detergent. That may eliminate or minimize the problem. My DD had rashes with some brands of diaper and good nights and similar are basically diapers. It is absolutely possible.
Perhaps try something like http://www.superundies.com/p-45-bedwetting-pants-nighttim...
FYI, I would expect dust to give her respiratory allergies,but other allergies to show up as rashes, tummy pain, headaches and nausea. I suspect that your DD has allergies not on the test. My DD is allergic to apples ONLY if she eats them. She can roll around in an orchard and be fine, but eat one? Bam! She's suffering. It does not show up on the scratch test but the allergist said to consider the history more than the scratch.