Or she could have just said “no thank you,” which is the same thing diabetics say when candy or other sweets containing sugar are offered. Why should an airline stop serving an item just because one or two people can’t eat it.
Read up on peanut allergies. Some children have gone into anaphylactic shock just from breathing air in a room where there were peanuts. Others have gone into shock from touching a desk at school where someone had previous eaten peanuts or peanut butter, even though there was no visible trace. There is no way to be 100% safe, but when an airline has told you it DOES NOT serve peanuts, it better not.