Your DDs experience sounds similar to mine when I was a teenager.
I'm only writing this in case it's of interest. I'm not suggesting I made the right choices.
I reacted to eating a chicken tikka sandwich from a 24/7 shop while walking home from a night club. My face swelled up, my eyelids swelled practically shut, my feet and legs swelled, had to rip my tights and shoes off. My throat swelled up and started whistling.
My neighbour was a retired nurse so she came to help me with antihistamine, but in retrospect probably should have called ambulance.
I visited gp who prescribed steroids, antihistamine and EpiPen. Referred to allergy clinic who couldn't find anything severe or conclusive, therefore I couldn't really seek to avoid anything food wise.
Carried on eating whatever I wanted over the following months, reacting to this and that, but not as bad as the first time. I was armed with my meds to immediately treat my symptoms and over the years my reactions tailed off.
Then years later I started to react to wine and beer, probably sensitive to sulphites?
I'm not a big drinker so if I took antihistamines before drinking the odd glass it was fine.
But then I developed hayfever and I am now sensitive to wood dust as I work with various timbers professionally.
Referred to allergy clinic again, still inconclusive, but the Dr. said it's fine to take antihistamines everyday so that's what I now do as there's always some kind of pollen or dust flying around that makes me react like I've suddenly got a terrible cold.
Lastly, if I haven't eaten something for a long time (years) and then eat it, I react to it for eg. recently that's been grapefruit, banana, persimmon.
Get the ball rolling and go to the gp, ask for allergy clinic referral and EpiPen in the meantime. Write a detailed food diary from now on so there is information to present to the clinic.
Good luck, it's scary, especially as it isn't happening to you directly.