The actress told the BBC that she felt that the role was 'too old' for her.
"My first reaction was 'Am I that old?'" the 46-year-old admitted at a screening of the film in London on Sunday night (October 21).
However, she said that director Mike Newell assured her that she was the perfect fit for the role.
"He said if you go back to the the book and work out the mathematics she is only 56. I said, 'Yeah but I'm 45', and he said it spans from age 27 to 56 - and I thought, 'What an original idea'.
"Then I found that Gillian Anderson was doing it [in a BBC TV version] and I thought, 'Not such an original idea!'"
The star also noted that she has played a very similar role before in Tim Burton's Corpse Bride.
"In a way I'd already played her because I'd done the [Tim Burton animation] Corpse Bride. I only played her as a puppet, but there were a lot of similarities."
The actress revealed that the wedding dress she wore in the film was one of her "favourite costumes of all time", noting that the role had in fact been 'right up her street'.
She was also awarded with the BFI Fellowship alongside husband Tim Burton this weekend.
Great Expectations will be released in the UK on November 30. Watch a trailer for the film below: