My hairdresser told me that Vosene Shampoo strips dyed hair of colour.....might be worth your daughter giving that a try for a few days.....failing that I'd do what redhead said and let the profs sort it out....
Black is the worst possible colour to strip from your hair. Bez is right about the vosene or any cheap shampoo because its quite harsh but dont expect too big a result. It will just look like a slightly faded black and it will take some time to fade too.I would get her down to the hairdressers and let them work their magic. Her hair isnt going to be in the best of conditions afterwards though. all the best.