Le Pen shared the gruesome images in December 2015, a few weeks after IS jihadists killed 130 people in attacks in Paris, sparking widespread condemnation in France.
A ruling said that the far-right leader had wrongly used parliamentary funds to pay an aide who was based at her party's headquarters in Paris.
French far-right leader Marine Le Pen proposed changing the name of her party to the National Union on Sunday as part of efforts to improve its image.
A far-right leader praised by Donald Trump; a scandal-hit conservative; a 39-year-old former investment banker; and a leftwing radical who campaigns by hologram.
Far-right leader Marine Le Pen and centrist Emmanuel Macron are the favourites to progress to a run-off on May 7.