I've never had siblings, I didn't grow up in a big family; it was just me and my single mom. And hectic family dysfunction was actually something that I craved.

Zajac. Debuting at the Sundance Film Festival the film won the Special Jury Award for Outstanding Ensemble Performance. In 2012 in addition to filming the third season of Shameless Rossum signed onto two film projects.

She currently stars on the Showtime dramedy Shameless as Fiona Gallagher. Her role in Mystic River (2003) garnered her wider recognition.