Snider was driving a BMW that hit an STM bus at the corner of 55th and Lindsay avenues on Aug. 14, 2012.
Her mother, 61-year-old Janet Stoddard Snider, and STM bus driver Sylvain Ferland, 49, were both killed in the crash.
The bus ended up on its side, and Ferland was pinned underneath. Seven other people were also injured in the crash.
Despite the two deaths, Snider is facing a single charge of impaired driving.
Crown prosecutor Lucie Martineau said a blood sample taken from Snider in hospital the night of the accident showed she had three times the legal limit of alcohol in her blood.
Snider's defence lawyer Pierre Joyal argued that the sample was inaccurate and may have been obtained without a warrant.
The trial will continue before Judge Thierry Nadon.