The car crashed into a cafe window, trapping the customers inside and pinning the mother-of-three to the wall.
Her husband and kids were also injured in the accident and police and paramedics were called at around 1.55pm on Sunday. Several fire crews fought to free the woman while attending to her husband.
The mother had "potentially life-threatening" injuries while the father sustained a serious head injury. They were both taken to Royal Sussex County Hospital, in Brighton. The children suffered shock and minor injuries and so did the female driver. They have been taken for treatment at the Conquest Hospital, in St Leonards-on-Sea, where blood samples were taken from the driver for analysis.
Sadly, despite efforts to save her, the 37-year-old mother died of her injuries today. The police are investigating the driver to decide if she had been under the influence of alcohol at the time of the crash.
Sergeant Peter Verney, of the Sussex Police roads policing unit, said:
"Our thoughts are very much with the family at what is a very difficult time, and we would ask people to respect their privacy while they try to come to terms with what has happened."