So I suffer badly from psoriasis and don't have a clear cut fix yet myself. Part of the problem for me going carnivore is my wife is Italian, and asking an Italian to cut out all carbs from the daily meal is like asking a vegan to eat a steak. Also, I have to deal with gout as well, so both make the carnival diet a challenge, though I would like to try it for a while to see if it helps.

However I have found the following has helped reduce my flare ups (and these are all over me, my lower back is basically one huge patch):

• light: uvb in particular helps, but you have to clear the plaques off first or it's limited. I used to go to a standing sunbed once a week for 12 min and it nearly cleared up entirely back then. Since covid though there are none in my area now so that's out for me.
• stress: it is an auto immune disorder, and stress is a huge trigger. My first flareups were in my teens properly and it was due to the stresses at school. Now I'm living in a high stress situation constantly, and it's making itself known a lot for me, but finding ways to manage and reduce stress are key. Doesn't help when it's the psoriasis stressing you out either 🙄
• food: I have noticed it is worse with certain foods the previous day. Oddly enough I have more trouble in the uk than the us for this though, as it was clearing up in places it had been for years when I was in CO for roughly three months (that was a high stress time too so it made zero sense). However in that time in my diet changed a lot
• cbd/weed: further to the CO period I recently had, tbh I was enjoying the rocky mountain highs as it were to help with managing my father passing, which might have contributed. That was something I had been indulging for decades prior and to be frank it was a lot better back then.

I can't speak to the pesticide issues or a no carb/grain diet, but if those work for your DIL let me know so I can push for more steak and potatoes my side 😂 rooting for her as a fellow sufferer!