The song is set for release March 18. It will be included with five other songs on a digital EP later this spring through Genius 4Ever Records.
"'P.S. I Love You,' which Rachelle wrote with co-writer and producer Chris Seefried, is essentially a love song from Rachelle to her husband," a news release from her record label said. "Beautiful, yet haunting lyrics depict two profoundly tragic moments of the producer's life -- the deaths of his father and his son."
Phil Spector's father committed suicide when Phil was a child and Phil's son died of leukemia when he was 9.
Rachelle's label said "P.S. I Love You" is intended to be reminiscent of Phil's classic song, "To Know Him is to Love Him."
"I would always sing 'To Know Him is to Love Him' to Phil and I wanted to do something that paid homage to Phillip's losses. Through this song, I wanted to humanize Phil and show compassion to him as a person, who dealt with a tremendous amount of loss in his life, but was able to achieve so much. And if people only knew him like I do, they would love him, too," Rachelle Spector said in a statement.
She also is working on a stage musical about her husband's life.
Phil Spector, 73, is serving a 19-year-to-life sentence in California's Corcoran State Prison for fatally shooting actress Lana Clarkson in his Alhambra home in 2003.
The music producer married Rachelle, now 32, in 2006.