You can just call me Tots. I would say Deb, but we already have one, and I don't want to be a Number 2 in anyone's mind.
Stress can be a cause. I was hoping they didn't say that, because I didn't want you to worry too much. Check out where her hives are. If she has them bad on her feet, have her wear different shoes, more loose fitting ones, and flats, no heels. That takes care of the pressure thing. Same with tight waistbands. That should give her some relief.
FWIW, I am only allergic to cats, and I don't have one. I do get better results with my laundry now that I use Bio-Kleen. It is a phosphate free cleaner. I can get it at Sprouts, Elliotts or Whole Foods, so you should be able to find it. But, truly, the pressure, and CALM is the easiest to take care of. Well, the pressure anyway. Once the prednisone zaps out the worse hives, it should be manageable with the zantac, and whatever else works. That is more of a hit or miss.
Suggestion? It might help if she thought she had control over this situation. As I am sure you have realized by now, there are many different things that can trigger, and many other things that can help or hinder any improvement. Maybe if she were given the different ideas, she could use herself as some kind of scientific experiment, solving her hypotheses, so to speak? I dunno, just trying to give a different spin, so she doesn't feel so danged miserable..