Two months later, she was at the vanguard of the protest movement, standing before 80,000 demonstrators who had been chanting “Russia without Putin.”

In an interview, Ms. Sobchak said she did not dwell much on what she risked by speaking out.

“If you see a boy being beaten in a dark alley, you will not pass by, you will stop and try to defend him, though you realize that you may be beaten too,” she said. “A person doesn’t want to feel like scum, and this is what happened to me. I realized I could not participate in this unfair monkey business anymore. And I quit.”

Ms. Sobchak’s speech to opposition demonstrators in December did not go over well; knowing of her ties to Mr. Putin, many protesters doubted her sincerity and jeered when she went on stage. The criticism was harsher in some St. Petersburg circles, where her stance was seen as a betrayal of Mr. Putin.

“On a human level, it is inexplicable — there should be gratitude toward someone who has done so much for her father, for her and for her mother,” said Mr. Yagya, 73, her father’s former aide. “The future will tell whether it was a mistake or not.”

Mr. Yagya added: “For her mother, it is a painful moment. I think for her father, it would be painful.”

Ms. Sobchak has gone out of her way to avoid personal criticism of Mr. Putin, but it is clearly painful for her as well. She has acknowledged that she can no longer speak about politics with her mother, a legislator in Russia’s upper house of Parliament, whom she called “the person I love the most.”

“Kinship is a very strong tie, a strong material,” Ms. Sobchak told Mr. Tkachenko, the talk show host. “But the ideas in my head are also of very strong material, so I have no choice. I have this feeling inside me that it’s all very complicated, but I make my choice and I never have regrets.”