The 43-year-old driver went off the road and hit a tree, which then impaled her windshield and pinned her down.
"I don't know how it didn't hit her. She's very very lucky," said Kristi Fry, who witnessed the aftermath of the crash.
Fry heard the impact from her nearby home and ran over to help.
"Her seat belt strap was choking her," Fry said. "She was kind of in a position where it was just wrapped around her neck."
Fry said a man driving a propane truck was following the van when it went off the road. She watched him use a pocket knife to cut the seat belt from the woman's neck.
"Her head kind of slumped down and then she took this big breath and then she started breathing at a kind of normal pace," Fry said. "She looked like she was sleeping, but before that her face was turning purple. It was kind of scary to see at first."
Fry and other witnesses stayed with the woman until firefighters arrived and used the jaws of life to free her from the wreckage.
The sheriff's department is now trying to figure out what caused the van to leave the road. Neighbors say the woman was on her way to pick up her children.
Her current condition is not known.