In 1996, Cassidy was nominated for the Most Promising Actress at the
Geneva Film Festival for her role in
The Sun, the Moon and the Stars. In 1999, she played the starring role in ''
Felicia's Journey, for which she was nominated Best Actress at the 20th Genie Awards. She was also nominated for an IFTA in 2005 as Best Actress in a Lead Role in Television for her role as "Maud Lilly" in the BBC BAFTA nominated drama Fingersmith'', In 2002, she appeared in the music video for
Coldplay's "
The Scientist". In 2011, she played Maureen in the TV film
Just Henry. In 2015, she played a main role of DC Dinah Kowalska in the
Channel 4 drama series
No Offence (2015–2018), In 2022, she starred as Rosaleen O'Donnell in the Irish film
The Wonder, alongside her own daughter Kila, who played "the wonder" and co-starring
Florence Pugh. She received a nomination for
Best Supporting Actress in a Film at the '
Irish Film and Television Awards in 2023. ==Personal life==