Erytab is an antibiotic also called "erythromycin" that belongs to the pharmaceutical group of macrolides. Its most common usage is as an alternative for penicillin in patients who are allergic to penicillin. It doesn’t seem likely to me that erythromycin can provoke the types of allergies you describe.

Allergies are immune disorders that are mainly genetically conditioned. People with an atopic constitution are very susceptible to developing allergies. Your friend could be allergic to erythromycin ... but erythromycin can't cause allergies to other substances. It seems that the fact that she developed various allergies after she stopped taking erythromycin is just a coincidence.

Furthermore, allergies are mainly incurable. The only thing that a person can do is to avoid substances that she is allergic to and to take anti-allergic drugs (antihistamines and corticosteroids) when an allergic reaction occurs. There is a therapeutic procedure for treating allergies called "desensibilisation" ... but there are certain risks during the procedure and success is not guaranteed. Your friend may consult an allergologist for an expert opinion.