Dr My 4yr Old Daughter Has Delayed Food Allergy. Tonite

Dr my 4yr old daughter has delayed food allergy. Tonite we went out and by mistake I gave her a prawns in bread crumbs thinking it was chicken. She is allergic to shellfish nuts and penicillin. I have just given her 5mls piriton chlorphenemine. She is now asleep with no symptoms yet. Should I be worried and can I do anything else.