Emergency crews were called to the scene of a single-vehicle rollover on Highway 3 near Monarch at around 7:30 p.m. Friday.
RCMP said an older pickup truck lost control on the eastbound lanes of Highway 3 and eventually rolled a number of times before coming to a rest on the centre median.
At the time of the collision, it was snowing and the roads were covered with ice and snow.
RCMP said there were three people in the truck. A 26-year-old woman from Lethbridge, who was on the passenger side, was ejected from the vehicle. The remaining two occupants, including a four-year-old girl, remained in the truck.
The four-year-old girl was released from hospital with minor injuries Friday night.
The woman was first taken to Chinook Regional Hospital in Lethbridge, then to a Calgary hospital to receive treatment for head and spinal injuries described as critical.
As of Wednesday, Dec. 28, she remained in the intensive care unit in serious but stable condition.
The driver of the truck, a 25-year-old man from Lethbridge, was not seriously injured in the collision.
RCMP continue to investigate what led to the crash.
With a file from Erika Tucker