NZ Lotteries Chief Executive Todd McLeay said the winner used her previous prize - in a different town to Dunedin - to buy a new car.
However the woman, who wishes to remain anonymous, says this big win will change her life.
"I have lived on coffee and nerves since watching the draw on Saturday night and realising that I had all of the seven winning numbers. It is so hard to believe that I could win Lotto twice."
The winner had kept the ticket hidden in her underwear drawer since Saturday, but also made a couple of photocopies to leave around the house - "just in case".
"Since winning Lotto the first time I still kept buying my weekly dip ticket. I am an optimistic person and believe that anything is possible - it also gives me a chance to dream each week as well."
She plans to invest the money, help out family members and give a sum to charity.
"And despite Marcus Lush suggesting on the radio yesterday that I should buy Dunedin's Larnach Castle, I have more modest plans, and would like to build my own brand new dream home in the future."
The winning Powerball ticket was sold at Dunedin Paper Plus and is worth a total of $10,845,530 million with $9,785,562 million from Powerball First Division and $1,059,968 from Lotto First Division.
The $10.8 million prize is the largest Powerball prize won in Dunedin since a $1.2 million prize was won in 2006, and is also the second largest prize won in the South Island since Lotto began.
After winning Lotto twice, the winner still plans to keep buying tickets, however she says that she will focus on winning Big Wednesday now instead.
