The 25-year-old actor made her debut in Dabangg opposite family friend Salman Khan.
She told The Times of India: "I'm eternally grateful for the fact that I'm doing what I like best. I thank my stars for it. I wonder why I wasted all that time being fat. I should have lost weight and started acting earlier.
"But as they say, things happen when they are meant to. Dabangg was the best start I could have got. From then on, it's been a combination of hard work, luck and everything put together."
Sinha added: "I was studying to be a fashion designer and despite being a star daughter, I had no intentions of becoming an actor. The phone call from Salman, offering me Dabangg, came out of the blue.
"I wasn't sure whether I would continue acting after my first film. But when Dabangg became a blockbuster and I got a positive feedback, I felt films were my calling. Before I knew it, I had signed on Rowdy Rathore, Joker and Son of Sardaar and I started to love what I was doing. Now, I am shooting 24/7."
Rowdy Rathore co-star Akshay Kumar recently denied that he is Sinha's industry mentor after appearing in four films with her.
She will be seen next in AR Murugadoss's upcoming Hindi remake of his hit Thuppaki.