O'Connor was the Democratic leader of California's second-largest city from 1986 to 1992. The two-term mayor was elected San Diego's first female leader after eight years on the City Council. She was married to Robert O. Peterson, founder of the Jack-In-The-Box restaurant chain.
Prosecutors said her gambling winnings amounted to more than $1 billion from 2000 to 2009 but she lost more than that.
Her defense attorney estimated the debt at $13 million.
O'Connor gambled in Las Vegas, Atlantic City, N.J., and San Diego.