She told Company: "We had no idea just how big it was going to become.
"The audition was top secret so all I had was: 'Vampire, 18, girl'. I was like, 'What am I supposed to do with this? Are there any directions?' Then my managers were like, 'Oh yes, there's a book'."
A day before the first audition, she cram-read the first two books: "By then, I really wanted to be Alice and I worked day and night getting into character.
"But it wasn't until we got to Portland to rehearse that I realised this thing was going to be huge.
"We hadn't even started filming when my mom called and said, 'Do you know you have a fan site?'"
On working with co-stars Robert Pattinson, Kristen Stewart and Taylor Lautner, she said: "I mean you hear the horror stories of people not getting along on set. And all of us have such severely different personalities but we all meshed and got along so well.
"I think the experience is so crazy that it bonded us. Now we really look forward to award shows because they bring us all back together."
However, the Twilight Saga: Breaking Dawn - Part 2 actress said she keeps herself grounded with childhood friends: "I honestly don't have a lot of friends that are actors. Most of my friends I've known since sixth grade and are out of the industry.
"It gives me a sense of reality rather than surrounding myself with a bunch of actors."
"Whereas if you're at home, walking down the street you probably won't. It's something I've learnt to navigate my way around but I try to keep my private life private."
Regarding her love life, she joked: "You know, my brother won't walk out of a restaurant with me anymore because he doesn't want to be linked to me as my new 'mystery man'.
"Same with my close guy friends. In the beginning, my mom would be like, 'Are you dating this person?' And I'm, like, 'Mom, no! If I'm dating someone, I will personally come and tell you'.
"It's kind of insane that you can literally be walking beside somebody and not even know them, but you can still be dating them. It always makes me laugh."
Finally, on her maturing style, she said: "My style has definitely evolved. When I first started out I think I was a little all over the place and the clothes kind of wore me rather than the other way round.
"But now I'm at the point where I'm comfortable dressing for me, I know what works and what I like. Give me a great pair of skinny jeans, a T-shirt and a black blazer, teamed with an amazing Chanel necklace and great bag, and I'm happy!"
The Twilight Saga: Breaking Dawn - Part 2 will be released on November 16.
Watch a clip from the film below: