It has become insanely common to read stories where someone feels as if some people were doing things on purpose to bother them. As if they were actively looking for ways to make their life more difficult. They even believe that this kind of attitude is coming from friends and family members. People that supposedly love them are out of nowhere acting in favor of making their life harder. You hear how insane that sounds? I don't know if this comes due to entitlement or if there is something deeper to all this. They really believe they are being damaged by their loved ones out of spite or something.
The story of u/alalufra seems to be just another example of how persecuted these people feel just because they are not getting exactly what they want the moment they want it. Even though the family was actively looking for ways to accommodate the allergies the sister's husband has. But the fact that they were going to provide safe foods and safe dishes to eat and stop the risk of getting in contact with nuts wasn't enough. By the way, this person does not have a problem with being near that food. So the whole birthday wasn't an issue whatsoever. The real issue was, in fact, the people invited. They are the ones who had a problem with the accommodations, not the allergy.
These people need to understand that nobody is trying to damage them. They were invited to the birthday party because they are well-liked by the family. They were going to receive accommodations because the birthday girl really wanted them to come, and they were kind enough to explain this even before they asked because of how much they appreciate them. But no, these people can only see the bad side that doesn't even exist to begin with. Whatever. Is best to uninvite them and avoid a bad moment during the birthday party. And even take this into account the next time the family is thinking of inviting them to anything.