The 3 Idiots actress, who portrays the turbulent life of fictional movie star Mahi Arora in Heroine, said sister Karisma was deeply moved by her performance.
"Karisma saw the film on Sunday night and after seeing her positive reaction, I felt I have done my job. She is my biggest critic. She was crying for ten minutes after watching the film. For me, that was the most special moment of my life," she said according to IANS.
Describing Kareena's performance, director Madhur Bhandarkar said: "She has never played a character like this and I am sure people will like her work. Her character is very complex and edgy. And moreover, Heroine is an intense but a very entertaining film."
The 31-year-old actress, who is due to marry Saif Ali Khan on October 16, denied that she was avoiding discussion about her marriage in the fear that it might overshadow the release of Heroine, and said she would rather people talked about her films than her personal life.
"I have been hearing all kinds of news from people and everyone is asking about it but whenever me and Saif will plan to do it, our fans will get to know about it 100 percent," she said.
"This is not the right time to talk about it. I want people to talk about my work and films. Whenever we decide, we will never hide."
Heroine also stars Randeep Hooda, Divya Dutta and Arjun Rampal, who said that Kareena had "given her all for the film".
The film, which releases on Friday, September 21, has been described as a career-defining role for Kareena.