The facts from a legal point of view.
She can choose her clients, her working conditions, and her rates.
Yes, she may refuse any client for any personal reason — including ethnic origin, age, gender, weight, etc. — without it being considered illegal discrimination, since the service is based on her personal consent within a private context.
However, if she refuses a client on an ethnic or racial basis while working for an agency, this could be considered illegal discrimination, because the agency offers a public service. Both the federal and provincial Human Rights Charters apply to businesses.