It happened during a baton pass two years ago. The daring move involves two horses and their riders charging at a full gallop toward each other, then passing within inches. But instead of passing, Christianson and her teammate collided.
"I could just remember catapulting into the air and knowing when I land, it wasn't going to be good," said Christianson.
Christianson fractured her fifth and sixth vertebrae, and bruised her spinal cord. She was paralyzed. And knowing her horse-riding days were behind her, she was overwhelmed with sadness.
"It's my everything. It's what I've only done. I don't know any different. I have to ride to be happy," she said.
She had seen actor Christopher Reeve's valiant efforts following his riding accident, and she was inspired to take action.
She learned about a paralyzed rider in Texas who developed a special saddle. He eventually made one for her.
It now takes four people to get Christianson situated in her high-backed saddle, which has a belt that keeps her strapped in.
Once on the saddle, a feeling of lightness overtakes her.
"I feel free. I feel like he's doing the walking for me," she said of her horse. "If I can't move my legs, he can do the walking for me."
The reins fit over Christianson's wrists since she doesn't yet have full use of her fingers.
"I'm telling him, neck reining, telling him to go with my arms," she said.
She used to fly down the arena on her horse. Finding an easier pace has taken some adjustment.
"It's different," she said. "It's hard because I want to go fast."
Whatever her pace, Christianson's mother is her biggest booster.
"I was so scared at first, but now she seems so confident in it that really, it's exciting, exhilarating to see her do this," said Roxanne Christianson.
Trail-riding is Melanie Christianson's first goal. Next, she'll focus on returning to the gaming arena.
"I may not be as competitive as I was before, but I'm not going to let it stop me," she said.
She also hopes to return to her career as a property specialist for the Federal Aviation Association in the near future.
She is filled with determination, but Melanie Christianson admits overcoming the paralysis is slow-going. She dearly hopes researchers will find a cure.
In the meantime, she is back in the saddle again.