Reading between the lines it would only be legal if she is bona fide self employed and there is a sub-contract agreement between the parties (e.g. 20% takings to salon owner, 80% to chair holder) but it doesn't sound like this arrangement to me. The fact they are talking about wages, fixed hours of work, etc. and the individual still not fully trained, would imply an employer/employee relationship. The salon owners discussion to reduce the wage could be seen as a variation in the contract or even a redundancy situation with a switch to self-employement.
Glad it's resolved, but if it isn't, consider going to the CAB as others have said for better advice. The problem at this level of pay and in this economic environment, even if the salon owner goes through the motions and does it all legally and by the book, there's not a lot the employee will be able to do other than make sure they get everything to which they are entitled vis a vis redundancy, notice of change, etc.