The 'Secretary' actress said she is not sure what kind of character she would play on the show which also stars Michelle Dockery, Maggie Smith and Hugh Bonneville, reported Digital Spy.
"I love Downton. I would totally love to be in it. But I don't know how I would fit in.
"There is this parlour game where people say who they would be and a friend said she would of course be Lady Mary. She said I would be the cousin who sleeps with everybody! A rich English playgirl!," she said.
"I chose this because of the script. I had never read a script with a woman like this. I thought I was going to trust it. It is such a scary thing (the Middle East) for most people to talk about that I think people are hungry for ways to sit and think about it. I have never been more proud of anything I have ever worked on.