"I love the work and if I die, know that I'm doing precisely what I want to be doing," she wrote in an e-mail to a friend Jan. 21.
Holland was one of three civilians killed Tuesday after several gunmen posing as Iraqi police officers stopped her vehicle at a makeshift checkpoint near the town of Hillah, about 35 miles south of Baghdad.
Holland and a second victim were the first U.S. civilians working for the U.S. occupation authority to be killed in Iraq, reports CBS News Anchor Dan Rather.
The identity of a third victim, a translator, was not immediately released.
Holland's family believes she was targeted by assassins because of her work, which included opening women's centers around Iraq.
"She was a lover of democracy," said her sister, Vi Holland. "She was a humanitarian. She believed our greatest chance for democracy (in Iraq) was through people who were most oppressed."
L. Paul Bremer, the top administrator in Iraq, has requested that the FBI investigate the slayings. It was not yet known whether the gunmen were specifically targeting coalition officials.
Holland, a 1996 graduate of the University of Tulsa College of Law, worked at two law firms in Tulsa before joining the Peace Corps and traveling to Namibia.
She returned to the United States after the Sept. 11, 2001, terrorist attacks, but did not stay long.
Tulsa attorney Stephen Rodolf, who kept in touch with Holland through e-mail, said she seemed to be aware of growing threats to her safety.
"We stand out, and those who dislike us know precisely when we come to town," she wrote to him.
Her job required her to travel almost every day on highways where snipers and roadside bombs lurked. And yet, she asked to travel with an unarmed escort because she felt the high security around her was a barrier to her work with Iraqi women, he said.
"She would not take foolish risks," Rodolf said. "But a big part of her commitment was that there are risks in the world, and if you are to accomplish good, you accept them."