Early inquiries indicate that she was carried on the bonnet of the other car and fell from the bonnet and was in collision with a Belisha beacon. The vehicle drove away.
Police subsequently attended an address in Barnet and arrested a woman in connection with the inquiry. She was taken to a north west London police station and was subsequently bailed pending further enquiries to a date in late April.
Witnesses or anyone who has information can contact the incident room on 020 8247 7821 or Crimestoppers on 0800 555 111.
More top news
Britain's stance over taking in more refugees could hurt David Cameron's EU reform plans, a spokesman for Angela Merkel's alliance has said.
The inquest into the deaths of 11 people in the Shoreham air disaster is due to be opened and adjourned today.
Criminals are escaping arrest because police are delayed in getting to crime scenes in cars that do not have sirens, officers have warned.