My daughter has experienced skin allergic reactions to five different types/fams of antibiotics.

This saga started when my daughter was 2 years old. Today she is 9. She has had two severe reactions to penicillin - the first was undetected as such (she broke out in head to toe (and I mean head to toe) hives) and with the second, which was much more severe, she was diagnosed with serum sickness. The next time she needed an antibiotic, she was given a Cephalosporin (sp) and after a few days of treatment broke out in hives on her trunk. We discontinued the antibiotic and luckily her strep throat was "cured". The next time she needed an antibiotic, she was given a sulfa drug. After five days of treatment she broker out in a rash up and down both of her legs. Again we discontinued the antibiotic and luckily her strep throat was "cured". We went to an allergy specialist. She did a drug challenge with Zithromax which my daughter handled without a problem. Next time she needed an antiobiotic, we gave her Zithromax. Guess what? A few days into treatment, hives. We stopped the treatment, she recovered and we've been healthy since. This weekend she contracted possible pink eye (doctor wasn't sure but a friend has it). He gave her Cipro (the only eye drop he could find with none of the previously tried antibiotics). I have her one drop yesterday - ONE TEENY TINY DROP - and one today. This afternoon she broker out in hives on her arms and trunk. I need some answers or ideas as to what might cause this because I'm really worried about what we'll do if she gets really sick.