The 51-year-old says she wasn't always such a joy to work with and in fact, she used to behave more like her on-screen alter ego.
Jane, who hosted the 63rd Primetime Emmy Awards on Sunday, said: 'I was terrible. It was so Psychology 101 - I felt terrible inside and I projected it on everybody else. I made everybody bad, wrong.'
She added to Access Hollywood: 'I was kind of shaming and humiliating, not unlike Sue Sylvester, so I had a lot to draw on.
'I wasn't a nice person to have around. And I can say today, I am kind of a nice person to have around!'