The girl was taken to a London hospital following the collision which happened while she was walking in Watling Street, near the junction with Meadow Way, shortly after 6.50pm on Saturday 10 July.
She died on the evening of Monday 12 July.
A man in his 50s, who was driving a yellow Audi S1, was arrested prior to the girl’s death on suspicion of causing serious injury by dangerous driving and driving while impaired. He has since been bailed until Tuesday 3 August.
Officers would like to talk to anyone who witnessed the incident, saw the pedestrian or vehicle prior to the incident, or anyone who has any dashcam, doorbell or CCTV footage.
You can call the Serious Collision Investigation Unit on 01622 798538 quoting reference HW/LB/60/21. You can also email firstname.lastname@example.org