Allergies are tricky things. People have different levels of allergic reactions, ranging from rashes or itching all the way to anaphylaxis. For many people, the severity of their reaction is related to the amount of exposure to the allergen. Allergies are different for each person. For example, some people with peanut allergies have to be in contact with the peanut, while others only need to breathe in the dust from the peanuts. Without knowing this person’s history with eggs and why she was told she was allergic, you can’t necessarily come to the conclusion that her allergy isn’t real just because of this.
Allergies can also develop over time and worsen over time. Something you could take/eat before may turn into something you can no longer have because you develop an allergy to it, so past exposure/ingestion also does not exclude newly diagnosed allergies.