An 18-month-old girl who survived a deadly car crash is reportedly improving after spending 14 hours strapped to a seat upside-down while hanging over a frigid Utah river, officials said Monday.

Lily Groesbeck's condition was upgraded from "critical" to "stable but critical" at a Salt Lake City hospital, after her mother was found dead in the car, NBC News reported. "She is doing remarkably well considering the circumstance. The doctors have been hopeful so far," Jill Sanderson, the mother’s sister, reportedly told local news station KSL on Sunday. "We would like to express our appreciation to the Spanish Fork rescue team for saving the baby's life."

The car was discovered on Saturday afternoon by a fisherman in the Spanish Fork River in Spanish Fork, about 50 miles south of Salt Lake City. Investigators said they believe the wreck occurred around 10:30 p.m. Friday, which is when a local resident reported hearing a noise, Police Lt. Matt Johnson told NBC.

The girl was found hanging upside down above the river, which flowed through the car but was not high enough to touch her, authorities said. It is not known how the car left the road, and the Utah Highway Patrol is assisting in the investigation.

Temperatures while the girl was trapped in the car fell to the low 30s overnight.