She resigned from the Liberal caucus to sit as an independent in March 2004 because of a dispute with the party leadership concerning the sale of BC Rail to CN.
She was a key force in the creation of the Democratic Reform BC party, which was officially founded on January 15, 2005, and became its first MLA four days later.
On May 17, 2005, Brenzinger was defeated by New Democratic candidate Bruce Ralston in her Surrey-Whalley riding.