In reply to tlm:
As I think was said above, it's not necessarily the company its the clients.
Where you are in a situation where you work with a limited number of people then its less of a problem, clearly.
If, however, you are being sent out to clients and potentially in meetings with hundreds of people per year, the chances of someone taking exception are vastly multiplied, and hence can totally see why a company would have an adverse reaction to hair colour if by employing someone they are risking their income.
I would suggest if she is intending to end up at a professional services firm (solicitors, accountants) then I'd head for a normal hair colour, to start with at least.
In terms of high street store assistant, can't see the problem.