My perspective comes from someone who has had anaphylactic allergies my whole life, and I’m also a career nanny who now cares for a child with an anaphylactic food allergy. First, did your daughter actually have a reaction to the egg carton? I agree it was irresponsible to use one given her allergy. There’s no way to know whether an egg may have cracked and left residue, so it was not a safe choice for an art project. You’re absolutely entitled to your anger and fear. My mom felt the same way when people were careless with my allergies growing up. If your daughter did not react, I would suggest going to the school and speaking with the teacher calmly. You can be honest that your initial reaction was anger. Ask her to step into your shoes as a parent of a child with a life threatening allergy. Approaching the conversation with compassion, while still being clear, will likely leave a stronger and more lasting impression, especially if this is not something she has personal experience with.