Olivia Edohasim, nine, died when the black Toyota Auris she was travelling in hit a brick wall on Manchester Road, Altrincham, Greater Manchester, on 7 May.
Police have released two CCTV images of a Citroen and a Range Rover to encourage the drivers to contact them.
Although not involved, police think they may be able to aid the inquiry.
Police said a man, 45, and a girl, 11 - who were also in the car and are believed to be related to Olivia - are still in hospital but are "recovering well".
Police said neither the driver of the Citroen C3 or a dark coloured Range Rover Evoque have come forward to speak to police.
Sgt Brian Orr, of Greater Manchester Police, said: "We don't believe the drivers of these vehicles have done anything wrong or were involved in the collision."
He said new information about where the vehicles were may "jog some memories".
He said: "Moments before the collision the Citroen C3 is seen to be travelling along Stamford Brook Road heading in the direction of Manchester Road."
He said it was then overtaken by the Toyota car Olivia was travelling in near the park entrance of Trafford College.
The Citroen then turned left on to Manchester Road towards Sale.
The driver of the Range Rover Evoque turned right on to Stamford Brook Road from Manchester Road and passed the Dulux building.
Sgt Orr believes the Range Rover driver saw the Toyota Auris overtake the Citroen and flashed the main beam headlights at the Toyota.
The Range Rover then continued along Stamford Brook Road towards Turnbull Road.
Police are urging two drivers who may have seen a crash in which a young girl was killed to come forward.