Choice of legal business structure in France?

My wife is a market research specialist in the pharmaceutical industry. Until the end of May this year, she was employed by the French branch of a global research company. Since resigning at the end of May, she has been approached by the French office to take on work, beginning with a three-month project. She does not wish to return to work at the French office on a permanent basis. There are a number of issues:

• The French office of this global research company will be her only client in France.
• There is every likelihood she will be approached by the UK office to undertake freelance projects, working from France.
• Her turnover will exceed the limit imposed for micro-entrepreneurs. Her initial project alone will generate a gross revenue of 21,000 euros.

Given these circumstances, what legal structure do you recommend she should adopt?

The French office has said it was prepared to offer a short-term contract for this initial project. Is the best way forward, i.e to undertake short-term contracts as she is required and then simply declare her income in our annual tax return in France?

Most of her work will be conducted from home. All travel and accommodation costs will be reimbursed by the company.