"I saw her two days ago, and she was just doing fine," Witt told The Associated Press. "She was in excellent shape. She was mentally alert. She smiled frequently."
Born in 1894 in Shellman, Ga., Baines claimed the title of the world's oldest living person when a 115-year-old woman, Maria de Jesus, died in Portugal in January.
The oldest person in the world is now Kama Chinen, 114, who lives in Japan, according to Dr. L. Stephen Coles of the Gerontology Research Group, which tracks claims of extreme old age. Chinen was born May 10, 1895, Coles said.
The oldest person who has ever lived is Jeanne-Louise Calment, according to Coles. She was 122 when she died Aug. 4, 1997 in Arles, France.
Baines outlived her entire family, including her only daughter, who died of typhoid.
Baines worked as a maid in Ohio State University dormitories until her retirement and has lived at the Western Convalescent Hospital in Los Angeles for more than 10 years.
After turning 115 in April, she said, "Living that long is like winning the genetic lottery."
Nurses at Western Convalescent Hospital described Baines as a modest woman who liked to watch the "Jerry Springer Show" and eat fried chicken, bacon and ice cream. She refused to use dentures.
"I don't know how she does it. She only has her gums, no teeth," said Susie Exconde, the nursing director who found Baines dead in her bed at about 7:25 a.m.
Witt, her physician, said that when he visited Baines earlier this week, she only complained that her bacon was soggy and arthritis was causing pain in her right knee.
Baines celebrated her birthday at the nursing home April 6 with music, two cakes and a letter from President Barack Obama, whom she voted for in November.
Featured on local television newscasts when she cast her ballot, Baines, who is black, said she backed him "because he's for the colored." She said she never thought she would live to see a black man become president.
"We were hoping to have her until the next election," Exconde said. "We'll miss her."