quite possibly it is the PB but not the actually nuts... have you considered the preservatives/additives in the PB?

my dd reacts to some highly processed foods.(that colourful party popcorn is the worst) it is not immediate and it does not affect her mouth or breathing but it is definately from foods. she gets hives and itchyness and rashes.

in her case its not an allergy its an intolerance. so sometimes its ok if her body is not too overloaded a the time, but once she is eating processed food too much it starts to creep up on us again.

just a thought.... hth.