I don't think eating specific foods will cause allergies. I think some kids just have them since it runs in the family. For some allergies, I have read that environmental chemicals can cause allergies by lowering the immune system while the infant is still in the womb. I haven't heard of anything that you can do to prevent ever having allergies.
My whole family has allergies. I never really had them until after I had my second son. It's an immune system response. It's not an ailment or preventable. It can be treated by helping the body build the immune system with allergy shots.
If you've been eating peanut buttor for 6 months with no affect, then I would think you're fine. Perhaps you might wait to give the baby peanut butter straight until she's a year or two. The reaction is less severe when they're older. Most people grow out of the severe allergies gradually.
My brother had allergy shots since he was in elementary school. As an adult he no longer needs them. My father had severe allergies needing to take shots several times a day. After he moved, he rarely has any allergic reactions as all.
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