Emergency services were called to the collision between a Nissan Qashqai and Vauxhall Corsa on the A308 Marlow Road near Maidenhead on Wednesday.
The driver of the Vauxhall - a 38-year-old woman - was taken to hospital with life-threatening injuries and died in hospital on Monday.
A nine-year-old girl in the same car was taken to hospital with serious injuries and has since been discharged.
The three occupants of the Nissan all sustained minor injuries.
No arrests have been made in connection with the crash.
A woman has died from her injuries five days after a car crash in Berkshire.