"Chicago P.D.," and now she is more openly discussing that decision. Although she hasn't given a specific reason, she did recently reveal that she was "miserable" on the show.
As a guest on Refinery 29's podcast "Unstyled," Bush recounted how the gig had been her dream job but she came to see it as being trapped in a burning building. It turns out she wanted to leave by the time she finished the second season, but couldn't bring herself to do it right away. In fact, she remained on the series for another two full seasons.
Bush described herself as stubborn, leading her to stay on for at least part of that extra time. Additionally, there were many "wonderful aspects" -- including the fact that she "made family" on the show -- but ultimately that wasn't enough. Bush recalled sitting down with her bosses at the end of Season 3 and telling them, "If something really drastic doesn't change, I'm leaving at the end of the year."
She didn't say what she wanted to see change, but she did share the sense of relief she felt after having that conversation. That feeling led her to acknowledge how unhappy she was.
"It was then that I realized that I'd been drowning. ... I was just so unhappy and it was my dream job and I was miserable and I had to go," she said.
Beyond that, Bush wasn't comfortable giving "the specific breakdown of exactly why [she] left," but as she pointed out, she doesn't have to. Maybe she will at some point, or maybe not, but either way, she has moved on. News of Bush's exit came in May, and "Chicago P.D." Season 5 premiered in September without her. She has since landed an acting and production deal with 20th Century Fox Television, so we'll likely see her back on TV at some point soon.