Suggest Remedy For Itchy Skin Rash Post Amoxycilin Tablets

My friend was prescribed amoxycilin for dental infection 1.5 months ago. Within two days, a rash started that is now quite severe with severe itching, like hives. Lower energy ensued as the rash became bigger also occurred. She has tried probiotics, vessel care to support healthy methylation, vitamin D, Vitamin C, home made kefir, Benadryl and the rash keeps getting worse. I have read a little on this and it seems that she may be having an allergic reaction to the antibiotic. It has lasted so long, however, that I am now concerned. What would you advise? My email is YYYY@YYYY