Mourning the death of Anita, an Indian-American, Clinton said she knew her from her Senate days.
Anita, 41, died in the Mali hotel siege on Friday. She's the only American known to have died in the attack. A former Peace Corp worker in Senegal, Datar was in Mali on an international development project.
The casualty hit home for Clinton, the 2016 Democratic presidential front-runner and senator from New York for eight years.
"My prayers are with the Datar and Garten families, especially Anita and David's son. My heart breaks thinking of the burden he will now bear on his small shoulders and the courage he will have to show in the days ahead."
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"As I said this week, America must wage and win an immediate battle against ISIS, al Qaeda, and other terrorist networks, as well as a generational struggle against radical jihadism," CNN quoted a statement from Clinton as saying.
US Secretary of State John Kerry had mourned Anita's death last week.
"We mourn American Anita Datar and all those lost in Mali Attacks," Kerry had said on Friday.
"We extend condolences to family & friends and stand with the Malian people," he said.
Anita is among the at least 19 victims of terrorist attackers at the Radisson Blu Hotel in Bamako, Mali. More than 100 people were taken hostage. The rampage came a week after at least 130 people were killed in Paris by terrorists.