She was rushed to hospital after the crash in Upper Brighton Road where her condition is described as life-threatening.
Police, paramedics and London’s Air Ambulance raced to the scene at the junction with Croylands Drive at about 10am.
Passengers on the bus – three woman aged 23, 42, and 40 – were also taken to a west London hospital with minor injuries.
Police said the bus driver is assisting with their enquiries. The surrounding roads were closed for hours as police investigated but have since reopened.