Conn was born in Brooklyn, New York, the daughter of a clinical psychologist. "Didi" was her childhood nickname. She attended Midwood High School; her brother is opera singer Richard Bernstein. She has been married to composer David Shire since 1982, with whom she has a son, Daniel Shire, who has been diagnosed with autism. Conn is also stepmother to Matthew Shire, a Los Angeles screenwriter.
- She has a son, with David Shire, born in 1992.
- Mother of a son named Danny.
- Was considered for the role of Olive Oyl in "Popeye"
- She wanted to read the role of Rizzo at her "Grease" audition, but the producers decided that she was exactly right to play the part of Frenchy.
- Younger brother is bass-baritone opera star Richard Bernstein.
- She once attended a school play of "Grease" at Nyack Middle School (in the play, "Danny" was played by "Freaks and Geeks" star John Francis Daley). Didi signed autographs for the cast, crew and audience.
- Studied mime with Tony Montanaro in the first year of his Celebration Mime Theatre.
- In 2003, it was reported that she was a driving force behind a planned third Grease film. She was featured in the first two films as "Frenchie".
- Executive produced a children's animated series called "Didi Delightful," which will introduce a recurring character with autism.
- The mother of a son diagnosed with autism, she was named national celebrity spokesperson for Autism Speaks in 2008. She has also been a spokesperson for the National Alliance for Autism Research, now part of Autism Speaks. She has performed at benefits for Foundation for Education Children with Autism (FECA).
- Daughter of a clinical psychologist.
- Stepmother of Matthew Shire.
- Explained in a 2003 interview why her character Frenchy disappeared about halfway through Grease 2. She said when they began filming, the script was not even finished yet, but the draft they were using still had her character in it. However, the script was rewritten once again during filming, and her character had been written out, and she was told halfway through filming that she was no longer needed. Then, during the editing process, the filmmakers ultimately decided to include Frenchy in the final cut, though they had limited footage. Didi described the filming process as "rushed, frantic, and unorganized".
- Portrayed the character Stacy Jones in the children's television series, "Shining Time Station".