Cool compresses or ice packs should help. If your sister were actually allergic to some product or coloring, an uncommon but occasional occurrence, she would a lot more than burning--she would have a lot of
swellingAbdomen - swollen
Ankle sprain swelling
Breast - premenstrual tenderness and swelling
Foot swelling
Foot, leg, and ankle swelling
Gums - swollen
Joint swelling
Mastoiditis - redness and swelling behind ear
Scrotal swelling
Swelling, redness, and so forth. So although I'm not sure that the irritation had a specific cause, her doctor should be able to prescribe a topicval cortisone scalp
preparationPreparation h hydrocortisone like
clobetasolClobetasol propionate
Clobetasol propionate emollient
Clobetasol topical or betamethasone, which should alleviate the symptoms more quickly. As far as future treatments and perms, I wouldn't rule them out by any means, even after this. Her doctor will be able to advise her on this too.
Best.
Dr. Rockoff