Race preparation is the hardest. Not the training, which Van Deren does eagerly, but the packing. In stopping the seizures, her mind, otherwise sharp and unaffected, was robbed of part of its memory and organizational skills.

Her dining room table is covered with gear. She divides it into carefully marked bags that will await her at various aid stations, sometimes 40 miles apart, along the next course. Which bag needs a headlamp? Sunblock? Extra outerwear?

Van Deren can no longer read maps. Telling her to go five miles, turn left, then right, then left is a confusing algorithm. She rarely runs a race without a wrong turn. “Everyone knows not to follow me now,” she said.

Gerber, who works at Craig Hospital, a rehabilitation hospital in Englewood, Colo., for people with brain or spinal-cord injuries, said that Van Deren “can go hours and hours and have no idea how long it’s been.” Her mind carries little dread for how far she is from the finish. She does not track her pace, even in training. Her gauge is the sound of her feet on the trail.

“It’s a kinesthetic melody that she hits,” Gerber said. “And when she hits it, she knows she’s running well.”

Her family and friends offer full support. Still, they worry.

“I’m just terrified we’re going to lose her,” said Barb Page, executive director of the Craig Hospital Foundation.

Running was always the self-prescribed antidote to seizures. When Van Deren felt an aura, a tingling sensation that signaled an upcoming seizure, she would lace her running shoes and go out the door. She never had a seizure while running.