The actress appeared in the CBS sitcom as Helga, Colonel Wilhelm Klink's secretary as a series regular for the first season and then made two uncredited appearances later on. Lynn's other credits include Mission: Impossible, The Odd Couple, The Six Million Dollar Man and Bedtime Story opposite Marlon Brando. After Brando's death in 2004, Lynn's daughter Lisa Brando claimed the actor was her father.
Brando shared the news of the actress' death on Facebook: "My beautiful mother - Cynthia Lynn just became an angel in heaven RIP Mommy! I love you. I am so thankful that you were surrounded by the ENTIRE family and were not alone... The hospital room was over-flooded by people that loved you. I am So sorry that I was not there. I was on the phone and I KNOW that you heard me, when you eyes opened when you heard my voice......... You will me forever missed and NEVER forgotten..... XOXO."
Brando has organized a fundraiser to collect money for Lynn's memorial service. "She did not have any money and I KNOW that she wanted to have a CELEBRATION of life for her family and fans. She wanted to be sure that people celebrated with champagne and remembered all the great times and to not be sad upon her death."