Lily McCormick, who was a passenger on the gator utility vehicle, suffered life-threatening head injuries when it crashed on land near the coastal town of Looe on Sunday evening.
The girl, from nearby Liskeard, was airlifted to Derriford Hospital in Plymouth but was pronounced dead a short time later.
Devon and Cornwall Police said her death was “not being treated as suspicious” but that they had opened an investigation into “the circumstances of the incident”.
The male rider of the bike has been treated for minor injuries.
“Family and friends say they are devastated by the loss of Lily and are wearing a red ribbon around their left wrist in memory of her,” a police spokesman added.
“Red was Lily’s favourite colour.”
A candle has also been lit in her memory at the local St Neot Church.