Jean-Marie Le Pen was heavily criticised last week for writing on his blog that the Oslo government's "naivety" was to blame for the July 22 killings of 77 people in anti-Labour Party attacks by a far-right Islamophobe.
Le Pen accused Norway of not correctly handling immigration, one of the FN's central policy concerns – and something that obsessed Norway's self-confessed mass killer, Anders Behring Breivik.
"If I had disagreed or if I felt his words were shocking, I would have said so," Marine Le Pen, who has been trying to give the party a friendlier face since succeeding her father as party head in January, told Europe 1 radio on Friday.
Her father "raised the question, and it's a real question, about society's choices," she said.
The opposition Socialists' interim head, Harlem Desir, slammed Marine Le Pen's position as showing that "the party has not changed."
"Marine Le Pen has ended her silence but unfortunately (only) to justify the revolting," Desir said in a statement.
"By backing her father's words instead of firmly condemning them, Marine Le Pen is justifying the worst and insulting the memory of the 77 killed" in the Norway bombing and mass shooting, he said.