She said: "People would come up to me when I was eating with my family in a restaurant or something and I would always just curl up into myself in a ridiculous manner.
"My family would be embarrassed and it would be like, 'Kristen, what are you doing? Just be nice and say hello'. And I honestly don't know what my problem was.
"I think it's natural that 13 year olds can be pretty insecure, but what's unnatural about it was that I wasn't insecure. I loved talking to people normally. I was so engaged and outgoing. It's just fame. That's what I had a really hard time with."
Kristen - who is in a relationship with her 'Twilight Saga' co-star Robert Pattinson - admits she was a "freak" about public scrutiny and can understand why people thought she was a "weirdo".
She added in an interview with Radio Times magazine: "I was such a freak with all that stuff in the beginning. And that's way everyone thought I was such a weirdo. I was definitely overly self-conscious."