Food allergy ladies

I have a question for you.  DD has never had allergic symptoms.  She did have eczema as an infant, which is now completely resolved.  So, today we took her to Panera for lunch.  She had a PB&J sandwich.  She only ate maybe 2 or three little nibbles.  Kind of odd for her since she devours them at home.  Never a single issue with peanuts,  and she has had them many times.  She also had the Horizon Organic Blueberry yogurt Tuberz that come with Panera's kid meals.  She has never had that brand of yogurt, and never a problem with the yogurt she eats at home.  She ate the whole messy thing.  Within a few minutes, she had very red, itchy, watery eyes, and a visible rash on her cheeks and around her eyes.  She was scratching and complaining.  No other symptoms.  The itchiness and redness subsided about an hour later, without intervention, but we have been watching her.  I gave her Benadryl before her nap.

So, I am concerned that she has an allergy to something she had for lunch.   BUT, since she eats those things a lot, and without issue, I am at a loss for what it might be.  Do I try them one at a time on another day to see if I can figure it out?  Or should I jump right on having her tested?  I hate to put her through skin tests if this was a fluke.  What do you think?