The girl had to be treated in hospital for her injuries after an assault allegedly took place in the grounds of All Saints Church in Burton-upon-Trent, Staffordshire, on January 23.
The Independent Office for Police Conduct (IOPC) has said it is investigating Staffordshire Police's response to a number of prior incidents.
In a statement it said the inquiry followed a mandatory referral by the force, after the girl was admitted to Burton's Queen's Hospital for her wounds, last month.
Derrick Campbell, IOPC regional director, said: "As is widely known, the force is separately conducting a criminal investigation and a man has been arrested and charged in connection with that.
"Therefore it would be inappropriate for us to make any further comment at this time."
Claudiu Lucien Vacaru, 19, appeared before magistrates in January in connection with the churchyard incident.
He is due to enter pleas to charges of attempted murder, threats to kill and possession of a knife in a public place at Stafford Crown Court on Friday.
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