My 89 Yr Old Mother Experienced Out Of The Blue,

My 89 yr old mother experienced out of the blue, first scratching on her left ankle, then on her left calf, feeling extremely hot as if her insides were on fire. Face swelled, she was red all over and had generalized scratching including her scalp. She went to the ED and was treated with solumedrol and Benadryl. The only thing she ate was 3 hrs before--walnuts which she has eaten all her life and had some the day before. She took her HCTZ and K+ supplant about 30' before. She has been on these drugs for over 30 yrs. can this be a delayed reaction from eating the walnuts ? I think she must have been bitten by a spider and didn't know it. I worry that she should have been placed on an antibiotic because she also has a large and deep healing open wound on her leg. What are your thoughts and advice?