If she has a virus and was given penicillin they can get a rash which does not mean they are allergic to the medicine. I was waiting for DS to get the rash on penicillin 2 weeks ago. He was diagnosed with tonsillitis (hence the antibiotics) but came up monospot positive (glandular fever) which is apparently quite common in children and they often get swollen tonsils as a result, get started on antibiotics (penicillin usually) and then develop a viral rash. Although hives is different again.