My daughter is allergic to nuts.
She would need a different meal prepared for her, free from cross contamination. She would also need to trust the kitchen where this food was prepared. One trace of nut is enough to send her into anaphylactic shock and kill her (Thats the worst case scenario. There also minor symptoms such as hives, vomiting, red puffy eyes etc which she wouldnt want to happen either esp at a wedding)
Eating out is an extremely tricky thing for our family and we stick to restaurants where we know we are safe and can talk to the chef.
Not all prouducts list that they 'may contain' nuts and this is another problem within itself.
Luckily my daughter isnt airbourne allergic. If she were then she wouldnt be able to attend your wedding unless you completely changed the menu & cake to a nut free one (and that includes no may contain items).
My daughter wouldn't ask you to do this. She would tell you her requirements and then its up to you to if you change the menu or not. If she was airbourne there could be no comprimise. She would feel anxious attending even if she wasn't airboune as she is literally placing her life in the hands of people she doesn't know.
I understand this isn't your friends allergy. However looking at this from a parent of a nut allergic child, I see so many situations where my daughter is left out or has to be treated differently because she cannot eat what other children eat, that I actually have a lot of respect for your friend to say that she will not leave her partner out. Either they can both attend or none of them can.
I think you need to understand the seriousness of this allergy. It can and does kill. A 18yo boy died by the London Eye earlier this year because he ate a plain piece of chicken breast that was mistakenly cooked the wrong way, it had a trace of nut and he went into anaphylactic shock and died.
Either you can accomodate or not but don't blame your friend for being supportive of her partners life threatening allergies.