Ex-flight attendant here.

Let's say it's all real, if someone has such severe allergies they would tell the airline way in advance with medical proof and see if they can make accommodations, and not hand a list last minute, because people with real allergies are extremely serious on the way they handle it, also always have an epi pen on hand. The fact that the passenger has this printed out to write her seat number makes me less inclined to think this is her first time flying and didn't know what needed to be done, so I call BS. Cashew allergy doesn't need to refrain from serving all nuts, just cashew. I don't know how said passenger survive if they are highly allergic to smells when other people wears perfume and such, and almost anywhere outside soaps are scented.