Reddy, 73, rose to fame with her 1972 smash "I Am Woman," which became an anthem for the growing women's movement in the United States.
While one source says the progressive illness is in its early stages, marked by Reddy "asking same question every few minutes," another source suggested the symptoms were more advanced. She would forget where she put something and then suspect someone stole it, the second source said.
Reddy became a resident of the Motion Picture and Television Fund's Samuel Goldwyn Center for Behavioral Health in Woodland Hills, California, in June, both sources confirmed.
Reddy had been attempting a comeback this year, but her failing health forced her to cancel a concert planned for August 11 in San Diego. Her management kept the real reason secret, announcing that the show was "cancelled due to a scheduling conflict."
She did perform at the Orleans Hotel in Las Vegas for several nights in January. She earned great reviews for the Vegas shows.
"I am really in a very, very happy place," Reddy told a radio interviewer in January.
Reddy, who co-wrote "I Am Woman," earned a best female pop vocal performance Grammy for the record. She followed up with a dozen Top 40 hits over the next five years, including "Leave Me Along," "Angie Baby," and "You and Me Against the World."
A native of Australia, Reddy was helpful in launching the singing career of Olivia Newton-John.
She put her career on hold for more than a decade to return to Australia in 2002 to help care for ailing family members. She decided to return to the United States and the concert stage in 2012 after realizing she still had her voice when she sang for her sister's 80th birthday...