Hello... My Mom Was Diagnosed With Some Kind Of Allergic

Hello...
My mom was diagnosed with some kind of allergic reaction
She had this huge red scaly rash on her chest,up her neck and partially on her face and part of her face (mostly her cheek) was swollen
It didnt hurt it was just swollen...
She had been taking benadryl for a while which helped a lot with the rash (and the swelling too i think)
And she was also taking some kind of steroid stuff (the doctor told her to)
And one day she suddenly decided she didnt want to take the steroid stuff anymore because it was making her feel even worse (and making the rash come back) everything seemed fine yesterday...her rash had cleared almost completely and there was no swelling! But the next day her other cheek swells up! Is this really an allergic reaction to something or something else?? FYI she has been staying away from her potential allergens...
Please help...im really worried