She was 80.
Buskey, a friend of the family for more than 20 years, said the family was not “providing details at this time.”
Buskey, who first met Harper and her husband while working with them on her theater production of “All Under Heaven,” helped launch a GoFundMe account for Harper’s care earlier this summer.
Cristina Cacciotti said her mother died at 10:06 a.m. Friday.
Harper was cast as Mary Richards’ wisecracking best friend, Rhoda Morgenstern, and became so popular that she was spun off into her own show, “Rhoda,” midway through the flagship program’s run. She won four Emmys for the role.
The Rhoda character was originally conceived as an antagonist to Moore’s Mary, but was eventually fashioned into her outspoken friend. Harper recalled MTM executive Grant Tinker fighting to maintain those qualities in the face of early network concerns that Rhoda was too abrasive.
Harper returned to sitcoms in the mid-1980s with a self-titled show, “Valerie,” which cast her as a mother raising her children. But she was fired after two seasons because of a contractual dispute with the studio and network, and wound up suing for wrongful termination, eventually receiving a settlement of $1.4 million.
NBC kept the series — renaming it first “Valerie’s Family” and later “The Hogan Family” — with Sandy Duncan brought in to fill the void left by Harper’s character, who was killed off.
The actress did remain active — primarily in series guest work and made-for-TV movies — and played Rhoda again in a 2000 TV movie, “Mary and Rhoda,” which reunited the characters along with their grown daughters.
At the time, Harper recalled Moore telling her in regard to doing the movie — which was initially pitched as a sitcom revival — “Maybe we’ll fall on our faces, but let’s take a chance.”
Harper battled lung cancer and was subsequently diagnosed with another form of cancer, leptomeningeal carcinomatosis, in 2013. Her family recently started a GoFundMe page to help with the cost of her treatments.
Born in New York, Harper began her career as a dancer — performing at Radio City Music Hall in the 1950s — and later joined the comedy troupe Second City. She was also heard on the comedy album “When You’re in Love, the Whole World is Jewish,” a follow-up to the popular 1960s sketch piece “You Don’t Have to be Jewish.”
Off screen, Harper was active in politics and charitable endeavors, advocating for the Equal Rights Amendment and championing a charity known as L.I.F.E., which stood for Love Is Feeding Everyone.
CNN’s Sandra Gonzalez and Whitney Friedlander contributed to this report.