The girl was charged with "criminal conspiracy with terrorists" and "incitement to commit terrorist acts using online communication", on Monday, sources told news media.
Described as "very radicalised", she was detained in Melun near Paris on Thursday after investigators spotted a "very worrying" message on a group she administered on the encrypted messaging app Telegram.
She used the group to pass on "numerous" elements of propaganda from the Islamic State (IS) armed group and expressed the intention of taking action herself, the source told the AFP news agency.
Her home was raided and her phone and computer seized, although no explosives or firearms were found.
Telegram favoured by jihadists
Anti-terror police say Telegram, which is supported by Russian-born entrepreneur Pavel Durov, is a favourite means of communication for jihadists because of encryption.
The 19-year-olds who murdered French priest Father Jacques Hamel in his church on 26 July made contact through Telegram just a few days before committing their crime.
Two years for visiting terror-linked websites
A court in the cathedral city of Chartres on Monday sentenced Yannick Loichot to two years in jail, twice the term requested by prosecutors, for repeatedly visiting websites that incite visitors to commit terror attacks.
Loichot, who converted to Islam in 2009 and broke off with his family, visited pro-terror sites more and more often before the inquiry started and frequently watched videos of beheadings.
He also searched the web for ways to acquire weapons and hinted on his Facebook page that he wanted to destroy Paris's Tour Montparnasse skyscraper.
He claimed to have been motivated by curiosity.
The judge condemned Loichot to the maximum possible sentence.
Also on Monday Mauritinian national Aly Kebe was sent back to his country of origin because of "involvement in the radical movement and behaviour connected to activities of a terrorist nature" which made him a "particularly serious threat to public safety", according to Interior Minister Bernard Cazeneuve.
Two other men, an Algerian and a Malian, have been deported in the last week, and 82 since 2012.