I agree that you should do what is appropriate to protect your child. It sounds to me that you were reasonable in the way you brought the issue to the school and the PTA. Have the members of the PTA changed since last year, and if so, do they understand the potential severity of a nut allergy?
I have similar issues as my dd is lactose intolerant, and that just makes her sick, it's not life threatening. At a new playgroup, she was given a glass of milk because they had run out of forms on which I would have drawn attention to the problem. At another playgroup, I find it really difficult to explain to other mums that she can't have cheese etc at snack time - last week a plate of cheese cubes was put on the table directly in front of her. I know some people think I am being fussy, but they don't have to deal with the sick child later in the day if she eats something she shouldn't.