My sister dyed her hair and it went wrong. we think it might be an allergic reaction. what to do?

Not enough info: We need to get a description of what reactions your sister has that you think she might have an allergic reaction. For hair dye, the common reaction is contact dermatitis due to sensitivity to PPD or parapolyethylenediamine allergy. In severe cases, the skin can form blisters and can get superinfection. Your sister need to wash off the dye with plenty of tap water and see a local physician soon.