LOS ANGELES — A former mayor of San Diego spent the last decade wagering more than a billion dollars at casinos across the country, eventually liquidating her savings, auctioning her belongings, selling off real estate, borrowing from friends and taking more than $2 million from a charity set up by her late husband, a fast-food tycoon.

The former mayor, Maureen O’Connor, 66, blamed an addiction to gambling aggravated by a brain tumor for the gargantuan spree. Her lawyers said that while she had made well over a billion dollars in bets at casinos in Las Vegas, Atlantic City and San Diego, her actual net losses were around $13 million.

Federal prosecutors said it was impossible to know precisely how much Ms. O’Connor had lost over those years, but she emerged with her fortune gone and her health shattered. She took out second and third mortgages on her La Jolla, Calif., home to pay for the gambling.

The former Southern California political power broker, whose husband, Robert O. Peterson, founded the Jack-in-the-Box fast-food chain, appeared in court in San Diego on Thursday to answer to charges that she had stolen money from her late husband’s foundation to fuel her addiction.