She had done her research before booking. The salon had good reviews, a clean website, and a staff member who had spoken to her on the phone for ten minutes about her hair type before recommending the treatment. She felt looked after before she even walked through the door.

The treatment started normally enough. The product was applied, she was told to sit under the heat lamp, and she waited. Within minutes she felt something was wrong. A burning sensation across her scalp that she mentioned to the technician twice before anything was done about it.
By the time the product was rinsed off the damage was visible. Her scalp was red, inflamed, and tender to the touch in several places. She sat in the salon chair and was handed a mirror by a staff member who described what she was seeing as "a mild reaction" and told her it would settle down in a day or two.
It did not settle down in a day or two.

She spent the following week dealing with a painful, irritated scalp that required a visit to her doctor and a course of medicated treatment. She missed two days of work. She contacted the salon as soon as she was well enough to do so, explained everything that had happened, and asked what they planned to do about it.

They offered her 10% off her next appointment.
Not a refund. Not a formal apology in writing. Not an offer to cover her medical costs. A discount. On a return visit to the salon that had caused the damage in the first place.
She has not responded to the offer. She is currently exploring her options.