"She was like a 2-year-old child," her aunt recalled. "She was in diapers. I would have to sit on the toilet and tell her what to wash in the shower. She got better at doing things for herself little by little, but she had to be constantly reminded."

To convince her that her daughter had died, and to get her to remember permanently, Daubenspeck asked Melissa if she wanted to watch the video of Jasta's funeral, which Melissa - in a coma - had missed. Jasta was buried in a Cinderella dress.

Melissa watched repeatedly.

At first, said her mother, Melissa seemed detached, watching the minister tell everyone how Jasta loved to dress up in long dresses and high heels, how she brought her blankie to school, loved her pop-pop's French toast.

"Maybe it was so hard for her to believe. Or to process and comprehend," Daubenspeck said.

But the more she watched the video, the more emotional Melissa got. She would see teachers from her preschool, her sisters, touching the casket on the snowy ground and she'd weep.

And forget.

"To go through a death is bad enough," said her mother, "but to go through it over and over is, like, unbelievable. . . . I guess what happened as the time went on, and her brain was getting a little better, she could grasp a little of it."

By summer, Melissa Sweeney understood that her daughter was dead.

Medical explanations

Few are as lucky as Melissa. "Most people don't do that well when they come from such devastation," he said.

The brain, Fried said, "has nerves connecting all over the place, millions of connections . . . smaller than spiderwebs, connecting one thought to another."

Melissa's brain was shaken so violently by the crash that many of these connections were destroyed "in tiny areas diffusely throughout her brain."

"The blessing," he said, "was that she was 27, so her brain is going to have more plasticity, the ability to recover or form a new pathway."

Gradually, most function came back to her. But certain things never will.

For instance, Melissa can no longer do "times" tables. She was never a strong student, but these she knew by heart as a child. Asked to multiply 7 times 5, she counted out loud, "5, 10, 15 . . . ," and with each repetition held up another finger. When she got to her seventh finger and said, "35," she stopped.

She was far from confident of her answer.

Fried said concrete actions (making a sandwich, mopping a floor) are easier than abstract thought (multiplying in your head or creating a lesson plan).

Anjan Chatterjee, a neurologist and brain expert at the University of Pennsylvania, explained how short-term memory may be damaged.