Daly, 67, had been separated from Riordan.
Villaraigosa issued a statement saying, "The city of Los Angeles has lost one of its most dedicated and passionate philanthropists. Nancy Daly spent her life advocating for children and ensuring that our future generations are not forgotten. Her commitment to children -- especially foster children -- across the country led to the establishment of countless organizations, committees and even legislation for increased funding for children's rights. Nancy was a friend and inspiration to us all. She will truly be missed."
Daly founded United Friends of the Children in 1980.
UFC supports programs for foster children at Los Angeles County's MacLaren Children's Center; educational programs for children and youth in the foster care system; and the development of low cost transitional housing, career training and counseling, tutoring and scholarship programs for emancipated foster youth.
In 1984, she lobbied for and was instrumental in the creation of the Los Angeles County's Children and Family Services Department and Commission. She served as a member of the commission from its inception until June of 1999 and chaired the commission for two separate terms. She also worked to establish the county's Family Preservation Program and Committee.
In 1993, the mayor of Los Angeles appointed Daly to chair the Committee on Children, Youth and Families. The committee's report, "LA4KIDS," served as a blueprint on how the city could better serve its children.
Daly also co-founded the Children's Action Network, which sponsors an ongoing series of educational briefings for the entertainment industry with nationally recognized children's experts, and which also serves as a clearinghouse for the industry on children's issues.
The network developed national campaigns for immunization and childhood hunger.
On the national level, Daly was appointed to the President's Commission on Children in 1989. The Commission's report, "Beyond Rhetoric," served as a basis for more than fourteen bills in Congress.
In 2002, President George W. Bush invited Daly to the White House for his signing of the re-authorization of the Safe and Stable Families Act, which she had been instrumental in creating during President Bill Clinton's administration.
Daly had a long history of lobbying in Sacramento and Washington, D.C.,on behalf of foster children. She helped pass legislation to increase funding for health and mental health services for emancipated youth in California.
Daly chaired the Getty House Foundation, which manages the official residence of the Mayor of Los Angeles, from 1993 to 2001. In 1993, the Foundation completely refurbished the Getty House.
She was also appointed as co-chair of the Advisory Council of the Universal Access to Preschool Including Early Care and Education Initiative.
She was formerly married to Bob Daly, former head of Warner Bros. studios.