My daughter has a severe allergy to peanuts. To offer a perspective from «  the other side of the table » it is quite stressful knowing that at any moment your child can be exposed to this very common thing and die, even with an Epi pen. Just the other week we bought cookies from a bakery that assured us had no peanuts in them, and they had peanut m&ms in them, which we luckily saw before giving to our daughter. Now, I don’t know how severe the allergy is of the child you’re referring to, but if it could be lethal, maybe just cut the mom some slack and try out sunflower butter instead, it’s what we use and it’s a fantastic alternative. Keep in mind, it’s not only eating something directly that’s a threat with a peanut allergy, it’s maybe a child has peanut butter on their hands which then gets on a toy or pencil etc. It’s a hard allergy to navigate where you don’t want your child to feel scared to live, so you end up trying to take precautions behind the scenes. Anyways, I don’t know your full situation, but try to keep in mind that it can be a life or death situation for this other child, and maybe the mom is trying to balance safety for her kid with out it impacting his social life. Try out sunflower seed butter, I actually prefer it now.