Monterrey, Mexico (CNN) -- Even as Mexico's top transportation official said the plane carrying Jenni Rivera spiraled to the ground in a tailspin that may have surpassed 600 mph, some of the singer's family members were holding out hope on Wednesday.
The plane was flying at 28,000 feet when it began to plummet, Gerardo Ruiz, Mexico's transportation secretary, told reporters. It crashed in a mountainous area 9,000 feet above sea level, he said.
Determining what caused Sunday's crash could take up to a year, officials said.
Authorities were still working Wednesday to identify remains found at the crash site in a remote area of northern Mexico.
Rivera and six others were thought to be on board the plane, which lost contact with air traffic controllers soon after takeoff.
In California, the Mexican-American singer's mother said her grandchildren still think Rivera is alive.
"They continue thinking that their mother is OK, that God could perform a miracle," said Rosa Saavedra, noting she was trying to stay strong to support them.
Pedro Rivera Jr., one of the singer's brothers, said the family was waiting to read a document detailing her wishes that she had left with a sister about a month ago.
"She cannot read it yet, she can't say anything to us yet, until we are 100% sure that Jenni is no longer with us," he said.
Known to fans as "La Diva de la Banda" or The Diva of Banda Music, Rivera was well-established as a musical powerhouse with her Spanish-language performances of regional Mexican corridos, or ballads. For fans, the nickname captured her powerful voice and the personal strength many admired.
In recent years, she had been working to crack the English-language U.S. market and was reportedly on the verge of a crossover with a sitcom inspired by the success of "I Love Jenni," a Spanish-language reality TV show on Telemundo's mun2 network.
Rivera sold 15 million records, according to Billboard, and recently won two Billboard Music Awards, including favorite Mexican music female artist.
In October, People en Español added her to its list of the 25 most powerful women.
She performed at a concert in Monterrey on Saturday night before boarding the Learjet, which took off early Sunday and lost contact with air traffic controllers about 60 miles into the trip.
Just hours before she died, Rivera opened up to reporters about her divorce and the inner strength she found, thanks to her family.
"I'm so happy. So many strong things have happened in my life," she said. "I can't get up in the negative, which destroys you."
CNN en Español's Krupskaia Alis and Jaqueline Hurtado contributed to this report.