The actress, who plays Brooke Davis in One Tree Hill, sobbed when producers called her into a meeting and asked if she wanted to step behind the camera.
Bush has directed the show in the past, but insists it was "very poignant" to helm the second to last episode.
She recalls, "It was this weird thing where I was like, 'Why is everyone sitting down? I feel like I'm being called in the principal's office.' I burst into tears and acknowledged what an amazing honor that was to be trusted with that.
"Everything was really important and everything was really valuable. Because I knew that it was the last chance that I was going to have to tell these stories and to honor these characters and to really show their relationships. It just felt supremely important."
Bush admits she was an emotional wreck after filming wrapped in November, but she's beginning to enjoy having free time to herself.
She tells The Hollywood Reporter, "For weeks everyone stopped calling me Sophia and just started calling me waterworks everywhere I went. (Now) being able to walk my dogs in my own neighborhood and being able to see my family and see my friends that I grew up with that I didn't get to see for nine years has all just been great."