TOWN OF MUKWONAGO, Wis. -- A Wisconsin teen who ended up in a coma after being thrown from a speeding snowmobile has died.

Chelsey Lobenhober,17, of Vernon, was riding on the back of a snowmobile Wednesday when the driver lost control.

She was in a coma for three days. Town of Mukwonago police said that she died on Saturday.

Neither she nor the driver was wearing a helmet.

Authorities said the pair were driving across the ice of Lower Phantom Lake when the driver swerved to avoid a car on the lake. Police said they've received conflicting accounts of whether the car was parked or moving.

Police Chief Grant Turner said alcohol wasn't a factor. The driver hasn't been charged with a crime, but Turner has said that could change if drug tests are positive.