My 10 Yr Old Grandaughter Took Zithromax For What They

My 10 yr old grandaughter took Zithromax for what they suspected was pneumonia. After the 5th day she woke up with swollen face and lips. She then started with blisters inside her mouth. Now her blisters are all inside her mouth and on her tongue. She is off Zithromax. On Prednisone. Today she vomited. She's been to two children's emergency rooms. No one knows what is wrong. Could this still be a reaction to the Zithromax?