LEWISBURG, Tenn. -- A school bus ride got bumpy for a disabled teenager when she was toppled head-first in her wheelchair on Wednesday.

Video: Disabled Teen Hurt On Bus Ride To School

The incident happened on a Marshall County school bus, and the mother of 15-year-old Melanie Carter said she's furious not only that it happened but at how the school system reacted.

Carter, an eighth-grader, is defying odds that doctors set for her years ago: they told her mother that Carter would not live past 12 years old because of spina bifida.

According to the Spina Bifida Association’s Web site, spina bifida “occurs when the spine of the baby fails to close during the first months of pregnancy.” The effects of the condition are different in each case and there is no known cause.

Carter’s case left her paralyzed from the waist down. Her mother, Tisha Stocstill, said she was horrified after learning that her daughter had been flipped over headfirst in her wheelchair while riding on her bus.

"You know, I could've lost my child yesterday just dealing with what happened,” she said.

Marshall County school officials didn’t denying what happened, and transportation supervisor Glenn Ezell said he has been busy trying to figure out if the equipment on the bus failed.

It’s the responsibility of the bus driver and the aides on the bus to make sure Carter is securely strapped in to the bus, school officials said. Three adults were on Carter's bus: the driver and two aides.

“That's our main goal, to find out what happened to keep (it) from happening to another child,” Ezell said.

Carter said she ended up with a bump on the head and a few bruises, but doctors said she's OK.

“I'm still hurting a little bit, but it's not like it was yesterday,” she said.

Stocstill said that she realizes accidents happen, yet she's more concerned that no one took the immediate action of taking her disabled daughter to the nearest hospital and chose instead to have the school nurse examine her.

“A special needs child does need extra precautions. You never know what might happen,” she said.

Marshall County school officials are taking statements from all the adults to make sure rules were followed. Carter was less than excited about her next ride to school.

“I really ain't happy about getting on the bus again,” she said.

Marshall County's interim director of schools, Nancy Aldridge, said that about 16 students were on the bus with Carter, who was the only one in a wheelchair.