[citation needed] She was born to Pat, a mortgage underwriter, and Cecilia Rennison, a television researcher,[1] and was raised in Vancouver, British Columbia.

[citation needed] Rennison then landed a role in the John Dahl-directed Unforgettable (1996), with Ray Liotta and Linda Fiorentino, followed by the first of two Stargate SG-1 appearances as "Ally" in the episode 'Bane' (1998; S02E10), with Richard Dean Anderson and Christopher Judge.

[citation needed] In The Story of Us (1999), directed by Rob Reiner and featuring Bruce Willis and Michelle Pfeiffer, Rennison portrayed their daughter Erin.

Rennison continued to work on more Canadian projects such as the short lived but critically acclaimed These Arms of Mine for CBC, which landed her a Gemini Award nomination, and the Emmy Award winning casting director Coreen Mayrs' independent film A Feeling Called Glory (based on the short story "The Presbyterian Sidewalk" by Barbara Gowdy), for which Rennison won a Gemini in 2001, making her the youngest ever winner at 13.

After moving back home to Vancouver, she met Parker Bossley and began writing songs, which soon led to the formation of No Sinner, a rock/soul/blues outfit with drummer Ian Browne and guitarist Eric Campbell.