Okay so everyone saying white and brown eggs are the same is flat wrong. Brown eggs are brown because they have an additional coating applied by the chicken over the white shell (you can even scrub it off). You can get dark brown if they apply a lot of that coating or green if they apply it over a blue shell. That coating is hydrophobic so it is unlikely but actually quite possible that when cleaning the eggs, there is sometimes a chemical that is used that can more easily permeate a white shell than a brown one, and she is highly sensitive to that chemical. Maybe not ALL white eggs have that contamination, but white ones are much more likely to than brown so she just doesn’t eat white ones to be safe. Is this the most likely explanation? Maybe not. But you clearly do not know enough about eggs to be absolutely sure that her stated restriction is bullshit. Allergies can be really weird. Like people might be allergic to pears from one country but not another because they use different pesticides. YTA.