Jackie Stallone confirmed Filiti's death to the New York Daily News.
Filiti died Sunday at her mother's home after a battle with lung and brain cancer.
"I was holding her in my arms. I had just washed [her] face and told her how pretty she looked, and she just fell asleep," Jackie, 90, told the newspaper Monday.
Although Sylvester, 66, has been enjoying a career revival with his blockbuster movie "Expendables 2," he has suffered tremendous loss in his personal life this summer.
His 36-year-old son Sage Moonblood Stallone was found dead in Los Angeles July 13, about six weeks before Filiti died. The cause of Sage's death is expected to be disclosed following toxicology tests.
"She's too young to go, but she wasn't feeling any pain," Jackie said of her daughter. "What a terrible month. First Sage and now Toni. It's hard. At least they're together now in heaven."
Sylvester is Jackie's son with her first ex-husband, Frank Stallone, while Toni was her daughter with her second ex-husband, Anthony Filiti. She has been married to Stephen Marcus Lavine, a doctor, since 1998.