She spent the day being questioned by magistrates.
Francois Fillon was placed under formal investigation earlier this month.
The center-right candidate is accused of paying hundreds of thousands of euros to his family for work they did not do. Francois Fillon and his Welsh-born wife deny any wrongdoing.
Until recently, Francois Fillon was the favorite to win the elections, which will be held in two stages in April and May.
However, the former prime minister has now slipped behind far-right National Front leader Marine Le Pen and centrist Emmanuel Macron in the race to become president.
Francois Fillon, 63, faces accusations that he arranged for his wife to be paid public money for work as his parliamentary assistant amid claims that: the work she did was trivial or non-existent; Penelope Fillon had no parliamentary pass; few were aware Penelope Fillon was a member of Francois Fillon’s staff; misleading information was included on timesheets.
Francois Fillon is also being investigated over payments to his two children, Marie and Charles, when he was a senator. He has said his children were paid as lawyers for specific tasks, but neither was a qualified lawyer at the time.
In all, Francois Fillon is suspected of diverting public funds, complicity in misappropriating funds, receiving the funds and not declaring assets fully.
There are also questions about a job Penelope Fillon had at a literary magazine owned by a billionaire friend of the couple, for which she allegedly did little or no actual work.
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