Starting in 1925 she was music and drama critic for The Journal of Commerce. She was so well known for giving caustic reviews to what she considered bad performances that she earned the nickname "Acidy Cassidy." According to a 1993 article by the Chicago Reader, Rafael Kubelik, was "practically hounded out of town" by Cassidy. Cassidy had a particular aversion to touring companies of Broadway shows.
Although she was known for her harsh criticism, Cassidy's enthusiasm may have been even more powerful. According to Philip Rose, A Raisin in the Sun became a hit after a surprise positive review from Cassidy as well as "good reviews in other papers." In 1975, Cassidy was awarded the Joseph Jefferson Award. Her last published writing was for the 1990-91 Lyric Opera program book.
Cassidy was married to William J. Cassidy for 57 years. After her husband died in 1986, Cassidy lived at the Drake Hotel until her death in 1996 at the age of 96.