Do Pistachios Cause Puffy Eyes?
This is a classic allergic reaction. Very likely what happened is that she had a baseline allergy and after repeated exposure she eventually developed enough of an immune response to manifest itself now in the puffy eyes.
This is a sign that from now on she should avoid pistachios. She may possibly be allergic to other nuts as well so you may want to discuss this with her pediatrician who may refer her for allergy testing.
Right now as long as she is feeling well otherwise with no difficulty breathing or swallowing then you could observe and make sure she remains well hydrated and the swelling should resolve within 12 hours. If she is uncomfortable however you could give her 12.5 to 25 mg of benadryl - remembering that it could make her sleepy.
Thank you again fr the query. I hope my response is both adequate and helpful for you. If you have additional concerns I would be happy to address them.
Sincerely,
Dr. Galamaga