She says many live in poverty, work two jobs or don't have paid leave to care for themselves or children if they get sick. She calls on leaders to rethink public and corporate work force policies to better support single mothers.
"For many single mothers, this is the only world they know. Each and every day they make sacrifices, push through barriers, and nurture beautiful families despite the demands on their time and energy.
"I realise how extremely fortunate I am not to face the financial burdens so many single mothers and widows face. Poverty is one of the hidden and devastating aftereffects of loss for women."
She says public and private policies need to be examined to make sure they "embrace and support and love" all families, no matter how they fit together.
Sandberg's husband, Dave, died in a treadmill accident a year ago while on vacation in Mexico.
- with AP