Heigl was an original cast member and became the first series star to win an Emmy in 2007, but when she revealed she would not be entering the following year's Emmys race, she was deemed "ungrateful" - and quit the show soon after.
She told reporters at the time she did not feel she was given the material "to warrant an Emmy nomination" and withdrew her name from contention.
Because Katherine had started focusing on her film career following the success of comedy "Knocked Up", her remarks were seen as a slight to the show that helped make her a star.
In the new book, "How to Save a Life: The Inside Story of Grey's Anatomy", Heigl revisits her Emmy snub and her controversial exit from the drama.
"I thought I was doing the right thing," she is quoted in the book. "And I wanted to be clear that I wasn't snubbing the Emmys. The night I won was the highlight of my career. I just was afraid that if I said, 'No comment,' it was going to come off like I couldn't be bothered [to enter the race]."
With the benefit of hindsight, she now says, "I could have more gracefully said that without going into a private work matter. It was between me and the writers. I ambushed them, and it wasn't very nice or fair."
But she didn't expect to labeled "difficult," as rumors spread she had simply refused to show up for work.
Heigl has emphatically denied those stories, explaining she and her husband, singer-songwriter Josh Kelley, had just adopted their first child and she had already alerted the show's creator, Shonda Rhimes, that she wanted to leave and was just waiting at home "until I was given the formal OK that I was off the show."
Her career never fully recovered from the perception she was difficult to work with.
"The 'ungrateful' thing bothers me the most," she told book author Lynette Rice, "and that is my fault. I allowed myself to be perceived that way. So much about living life, to me, is about humility and gratitude. And I've tried very hard to have those qualities and be that person, and I'm just so disappointed in myself that I allowed it to slip. Of course I'm grateful. How can I not be?"
However, she added, "In this town, women who don't just snap and say, 'OK, yes sir, yes, ma'am' start to get a reputation for being difficult. I've decided it's not worth it to me to be pushed around so much."