My niece’s allergy is so severe that she’s not supposed to be in the same room with gluten products. You can guess how successful she is at making that happen consistently.
That may be a little exagered, and perhaps she can at least come in a church building.
But severe allergy is something serious.
My aunt has a mortal allergy to fish. She cannot eat, or even touch a product made with fish, or be in contact with an objecy with touched fish (contamination). In her house, nobody can eat fish at all, and they are very carreful yo not introduce any food that can have some traces of fish.
For family meetings we have to be prudent. One time, we have warned her that there will be a entree with fish. She was very upset. The danger is that someone may use the same knife for two different food.
To conclude, gluten is present in more food than fish. Flour is volatile and package never watertight. If there is flavor in her own house the niece will come in contact one day or the other…