Cassella's double degree in philosophy and women's studies led her to a position at a private boarding school in Connecticut teaching philosophy and religion. Finding that a private school teacher's salary inadequate, she attended law school. After almost ten years as a lawyer dealing with cases involving people with AIDS, transitional issues around marriage and bringing a test case for gay adoption to Connecticut, Cassella quit the legal profession and began her comedy career.
Cassella's stand-up comedy style was a mix of rants and raves. She found she could get an unlimited supply of material from just reading the news, Cassella settled in on her Because I Said So format of sit-down comedy tearing through news topics from law, entertainment, technology, religion, and finishing up with the things that she just found irritating. She has performed Because I Said So for 20 summers in Provincetown as well as in other places in North America.
Eventually, Cassella landed a full-time job and the love of her life. One of the original on-air talents on STAR!, she parlayed that job into her own talk show called Because I Said So.
In 2009 Cassella produced and hosted six episodes of The Vent!, a thirty-minute show she co-created and produced, that focuses on one topic from a variety of angles. Her production company, A Sweet Little Production Company, is located in Toronto and she continues to work on developing shows and films.
She is an out lesbian, and a frequent collaborator of US-based lesbian comedian Lea DeLaria. In addition to performing shows together, the duo have also cowritten a book and two screenplays. Cassella was a co-owner of The Flying Beaver Pubaret, a restaurant and performance venue on Parliament Street in Toronto's Cabbagetown neighbourhood until a fire on February 20, 2015 caused the venue to close for good.