i coloured a clients hair about a year after her chemo, she had started shortly after though with another hairdresser and found that her colour would take quite alot darker than she wanted, i done a strand test to be sure before colouring but found it was fine i wud do a all over tint and highlights. What i will say is her hair was very dry and frizzy in areas which was def her chemo hair as i could see it grow out and her natual hair that came though was so different. I would say do ask her to check with her doctor and then do a strand test and advise on some good haircare as her hair will be different to what she was used to.