NASCAR champion Greg Biffle‘s wife Cristina sent a harrowing message moments before the fatal plane crash that killed the couple, their family and three others, Cristina’s mother tells PEOPLE.

Just before her death on Thursday, Dec. 18, Cristina Grossu Biffle texted her mother Cathy Grossu, writing, “We’re in trouble,” Cathy tells PEOPLE.

“She texted me from the plane and she said, ‘We’re in trouble.’ And that was it,” Cathy says, crying. “So we’re devastated. We’re brokenhearted.”

The crash killed seven people in total: Greg, 55, Cristina, their son Ryder, 5, and Greg’s daughter Emma, 14 (who he shared with ex-wife Nicole Lunders); plus Dennis Dutton and his son Jack; and Craig Wadsworth.