The 26-year-old actress played Cinderella on the ABC fantasy drama's first season, but also stars in TNT's Falling Skies and upcoming ABC drama Last Resort.
Of a possible Once Upon a Time return, she told Small Screen Scoop: "You know what, I'm not sure because of the other shows. I know that it's an open-ended story as well because all of our characters are still living in Storybrooke."
Characters due to appear in season two of Once Upon a Time include Captain Hook, Sir Lancelot and Aladdin.
"They are introducing so many new characters like they did throughout season one," Schram confirmed. "There are so many of us in there, including Cinderella, and when the storylines match up to when she is needed, I'll definitely be there."
Once Upon a Time returns to ABC in the US on September 30. In the UK, Channel 5 is expected to air the new season in early 2013.