Ontario Provincial Police say Radika Nankissoor of Brampton, Ont., suffered fatal injuries after being ejected and trapped under the bus in Wednesday night's crash (on Highway 407) in Vaughan.
Six people were on the bus at the time of the crash, including two other Toronto-area women, aged 22 and 23, and the bus driver, a 66-year-old man from Hamilton, who were taken to hospital with minor injuries.
Two men on the bus, aged 18 and 23, also from the Greater Toronto Area, were uninjured.
GO Transit president Greg Percy described the bus driver as "experienced" with more than 15 years of service with the agency.
Percy told a news conference Thursday that the driver is recovering in hospital but said he could not give further details since the incident is under police investigation.
He called it a "tragic event for everybody."
"Our thoughts and prayers are with the families ... of the passenger who was killed in the accident as well as those who were injured, and the bus driver as well."
Percy said the vehicle was eight years old and mechanically sound. GO Transit has a "great safety record," he said, adding there has never been a death before in its history, on a train or a bus.
OPP Sgt. Kerry Schmidt said no other vehicles were involved and that it was too early in the investigation to determine the cause of the crash.
He said the highway was in good condition at the time, so investigators were looking into whether mechanical or driver issues may have been factors.
The bus, which left Hamilton at 8:30 p.m. and was headed to York University, went through a guardrail before rolling onto its side in a grassy median.