NEW YORK -- Katherine Heigl is still adjusting to the change in her "Grey's Anatomy" character, Dr. Izzie Stevens.

As "Grey's" watchers know, Izzie has been having an open affair with her married best friend, Dr. George O'Malley, causing a world of pain for his surgeon-wife, Callie.

"That was a kind of a big change for Izzie, wasn't it, after she was so up on her moral high ground," the 29-year-old actress said in Vanity Fair's upcoming January issue. "They really hurt somebody, and they didn't seem to be taking a lot of responsibility for it. I have a really hard time with that kind of thing. I'm maybe a little too black-and-white about it."

Heigl, who won an Emmy for her role in September, said she doesn't "really know Izzie very well right now. ... I'm trying to figure her out and keep her real."

Heigl also offers some critical remarks about last summer's smash comedy "Knocked Up," in which she co-starred with Seth Rogen and Paul Rudd.

"It was a little sexist," she said. "It paints the women as shrews, as humorless and uptight, and it paints the men as lovable, goofy, fun-loving guys. ... Ninety-eight percent of the time it was an amazing experience, but it was hard for me to love the movie."