Anne Mansouret told the French radio station RTL that her daughter Tristane Banon "considers the only way to end this is in fact to file a complaint, to say that at least justice can be done."
Banon's lawyer said he would file the complaint later Tuesday. Strauss-Kahn has labeled Banon's account "imaginary" and has threatened to file a criminal complaint of slander against her.
Strauss-Kahn is free on bail in New York, charged with attempted rape and other crimes after a maid accused him of forcing her to perform oral sex in his New York hotel room in May. The U.S. case has been badly weakened by doubts about the accuser's credibility.
Banon, 31, said on a 2007 television show that she had been attacked five years earlier by a politician during an interview in his apartment. She later identified the man as Strauss-Kahn.
"It finished very violently," she said on the television show. "I kicked him. He opened my bra. He tried to undo my jeans. It finished very badly."
Lawyer David Koubbi said Banon had been dissuaded from filing charges by her mother, a regional councilor in Strauss-Kahn's Socialist party. Mansouret now says she regrets urging her daughter not to file a complaint after the incident but she feared that would affect her daughter's career.
Banon came forward again after Strauss-Kahn's May 14 arrest in New York, but Koubbi said his client had no intention of pressing charges while the American prosecution was going on because the two cases should be kept separate. Banon is now moving forward, Koubbi told The Associated Press, denying that decision was connected to the weakening of the U.S. case.
"She's a young woman who's matured," Mansouret told RTL. "She took this decision, I suppose, after maturely reflecting."
Mansouret said she thought that by filing the complaint, it would help her daughter "rebuild herself."
"She tried to move ahead without doing that, and it wasn't possible. She arrived at a level of suffering. It's suffering to be permanently harassed by people who criticize how you've acted," Mansouret said.
Strauss-Kahn's lawyers said Monday he "has always said that the incident described by Ms. Banon since 2007 is imaginary."
"He notes that this complaint comes quite conveniently right at the moment when there is no longer the slightest doubt about the false nature of the accusations against him in the United States," attorneys Henri Leclerc and Frederique Baulieu said in a joint statement.
If Banon files her complaint, a prosecutor can conduct a preliminary investigation to determine if there is enough evidence to support charges against Strauss-Kahn. Preliminary charges are followed by a lengthier investigation, sometimes lasting years, to determine if the case should go to trial before a judge.
The same process would apply to the slander complaint against Banon.
A slander charge can be brought against anyone who French prosecutors believe deliberately filed a false complaint with authorities. In Banon's case, an investigation would begin only if her attempted rape complaint is found to be false. A slander charge carries a maximum term of five years in a prison and a 45,000-euro ($65,000) fine.
French prosecutors could decide not to pursue the case against Strauss-Kahn if they find evidence he engaged in forcible sexual contact that fell short of attempted rape. The statute of limitations on sexual assault charges in France is three years, while attempted rape charges can be filed for up to 10 years after the alleged crime.
Before the U.S. assault charges, Strauss-Kahn was considered the Socialist Party's strongest possible candidate to defeat conservative President Nicolas Sarkozy in France's 2012 presidential election.
Strauss-Kahn has relinquished his passport to authorities in New York and his next court appearance is on July 18.