Sheherazad Jaafari, 22, worked for Assad for the past year, advising him on how to cover up or lie about civilian killings, the New York Post reported.
Syrian rights groups are calling for Columbia to reverse Jaafari's admission into the School of Public and International Affairs masters degree program, which typically rejects four out of five applicants.
Alumni Haya Dweidary, the only Syrian in the 2012 graduating class, warned admissions officials about Jaafari.
"I was sure she wasn't going to be admitted because of her strong affiliation with the government and all the human-rights violations," Dweidary said. "It was completely shocking that she was admitted."
"We are outraged with what is happening at Columbia University," said Sarab al-Jijakli, spokesman for the National Alliance for Syria. "Columbia and Barbara Walters must ensure that they right the wrong and not accept someone from the inner circle of the [Assad] regime into their university."
Walters, along with Columbia Graduate School of Journalism professor Richard Wald, helped nudge Jaafari into the program. The Post reported Walters' influence was in return for Jaafari getting her an interview with Assad in Damascus in December 2011.
E-mail correspondence showed Wald said he would have admissions officials pay special attention to Jaafari's application.
Walters has since expressed regret for helping Jaafari, whom she previously praised as "brilliant, beautiful," calling her "dear girl" in e-mails.
Jaafari is under police protection because her father, Bashar Jaafari, is the Syrian ambassador to the United Nations.