The crash happened Monday when a train plowed into another one that was stopped.
Fifty-nine-year old Mary "Mandy" Doolittle worked for the American Nurses Association developing international outreach and helping with global accreditation for nurses.
Jeanne Floyd, the executive director of the association, called Doolittle a proud Texan who was the joy of the office.
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"She was not a nurse, but she was the face of this organization internationally," Floyd said. "She was a joyful, joyful individual and I can't underscore that enough."
Investigators are trying to determine exactly what caused the deadly crash. The moving train was operating in automatic mode, which means it was primarily controlled by a computer, although there is evidence the operator tried to slow it down. Since the crash, trains have been manually controlled as a precaution against computer problems.
Hersman said inspectors found 300 feet to 400 feet of markings on the rails, indicating some emergency braking took place before the crash. Hersman also has said the emergency brake control on the moving train was found pushed down, though it's not clear how or when that happened. The operator of the oncoming train was among the dead.
Hersman said investigators hoped to interview the operator of the other train on Thursday, a day after his release from the hospital.
NTSB officials say their investigations can take more than a year.