RCMP Cpl. Dan Moskaluk says the woman's vehicle, a Jeep SUV, fell nearly 250 meters down an embankment before it entered the river.
"The woman was belted in ... and she was very hypothermic when discovered," said Moskaluk.
Local firefighters and search and rescue crews worked for four hours in "a very complicated and exhaustive rescue effort" to extract the woman from the vehicle. The victim was airlifted to the hospital in Kamloops.
"However given her condition, due to the cold water ... she did succumb," Moskaluk said.
Authorities have not released the victim's name but Moskaluk says she worked as a nurse in Lillooet.