The European Parliament believes the money went to National Front employees working for the party in France rather than those working for the party's lawmakers in Brussels. She was also charged with complicity of breach of trust for her wider role as head of the party.
On March 10, Le Pen refused to answer their questions citing her immunity from prosecution as a Member of the European Parliament, leading the French prosecutors to ask the EU Parliament to lift her immunity, which it did.
Investigators suspect some National Front lawmakers used legislative aides for the party's political activities while they were on the European Parliament payroll.
Ms Le Pen ran for president in France's May election, on an anti-immigration, anti-EU platform.
Le Pen's lawyer said there was "no fictitious work" and added he plans to file a motion to dismiss the charges and end the investigation on Monday.
Le Pen denies the charges against her, but is now under active investigation concerning the appropriation of at least €5m ($5.4m).
Those pictures saw her placed under investigation for the "dissemination of violent images".
If tried and convicted, Le Pen faces up to three years imprisonment and a fine of up to Euro 375,000 (USD 425,000), although it is unlikely she would receive a custodial sentence.
Le Pen, the leader of the National Front, came a distant second during her bid for the French Presidency earlier this year, losing out to Emmanuel Macron. She had however promised to cooperate with the investigation after the May presidential and June parliamentary elections were over.
Some leading politicians are now living under a cloud of suspicion as to whether they misused funds meant to pay aides' salaries.
Macron himself is determined to avoid any possible connection to the lax or corrupt political practices of the past.