The band was returning from a competition in Pocatello when the crash occurred at about 7 p.m. MDT on Interstate 15, about two miles north of McCammon and 50 miles north of the Utah border.
Two students were rushed by helicopter to the Portneuf Regional Medical Center in Pocatello. Another 12 students went by ambulance with serious injuries, and 30 were taken by bus with minor injuries.
Only one student remained in the hospital Sunday evening, and she was expected to be released by Monday, hospital spokesman Brad Huerta told The Associated Press.
Police on Sunday also released the name of the bus driver, who remained hospitalized in stable condition. She is Debra Jarvis, 50, of Spanish Fork, Utah. Police said blood and urine samples were taken, as is customary in fatal accidents. The result will likely take weeks.
"We're trying to figure out why the bus went off the road," said Capt. Eric Dayley of the Idaho State Police in Pocatello. A phone call Sunday to Lake Shore Motor Coach Lines in Provo, the charter company that owns the bus that crashed, was unanswered.
John Miller, the band's director, was on a different bus but said he was told Christensen saw the driver slump over and leaped up to grab the wheel. He said Christensen's actions likely kept the crash from being even worse.
"She was doing what she loved - helping kids," Miller said. Members of the band met Sunday with Miller and his staff at the school to discuss the accident and whether they would participate in a Tuesday competition at Brigham Young University in Provo. A public memorial was to be held at the school gym after Miller and the students met.
"Considering everything, they're doing wonderful," Miller said. "They just had a really tough night last night."
Miller said 54 students were on the bus that crashed. A total of 222 students were on the trip, divided into four buses.
Idaho State Police officers said the crash scene initially was confusing and chaotic, with the other buses stopped nearby and family members steering their vehicles off the road as they came upon the scene of the tragic mishap. Distraught students sang church hymns after learning of the instructor's death.
"There were lots of young people milling about, with parents arriving," Dayley said. "We were able to come together and provide the needed medical attention and law enforcement services."
American Fork band member James Kimball, 16, was in the bus behind the one that crashed and witnessed the wreck.
"We were watching a movie, and I looked forward and saw the bus bouncing across the side of the road," the high school junior told The Salt Lake Tribune. "The bus flew off to the side, bumped across a couple hills and rolled over."
Kimball said the band, one of Utah's best-known, won the Pocatello competition. The school's bands have won the Utah state title for the past 19 years. The school band also performed at President George W. Bush's 2005 inauguration and marched in the 2007 Macy's Thanksgiving Day parade in New York.
Miller said he was getting calls and e-mails all day Sunday.
"It's just been powerful," he said. "The national band community is amazing."