The actress said that she is used to portraying "nice, sweet, fun" so found the character harder to play.
She said: "There really was no preparation. I was afraid to wrap my head around it, to be bluntly honest with you. It was a scary place to go. I'm not usually an actor that does that. I usually play characters who are nice, sweet, fun women. It was definitely scary."
Hewitt said that she found it difficult to control her emotions while filming the show.
She explained: "Before I got there, I thought that I was going to be able to have a lot more control over my emotions while doing it than I did. I credit the cast and the crew, and Mariska and Helen specifically, because they really pushed me."
The 31-year-old also revealed that she was able to connect with her character when she was "covered in blood".
She added: "I think I learned a really important lesson as an actress, that hair and make-up is great, but the lack of it is better. It really does something for you when you have to look at yourself covered in blood. I caught glimpses of myself and I was like, 'Gosh, I don't know who that actress is at all. I don't know who this person is'.
"Being able to have the gift that [executive producer] Neal Baer and everyone gave me of being able to not just strip down emotionally, but strip completely down - look-wise, wardrobe-wise, hair-wise, make-up-wise and all of that stuff - and be something that I've never been before, really allowed me, emotionally, physically and mentally, to go to a different place."