Why is Hillary Duff on Gossip Girl?

Why on Earth is Hillary Duff on Gossip Girl? I don't watch the show but I was recently watching E! News Daily and I saw that they were talking about her character. It's totally gay that they have her on now. I'm not sure if the show was ever good but they've reached the "jump the shark" zone. I didn't even have to watch the show to figure that part out. Congrats.