Mrs Williams was surprised at having made the winning bid of $156,000 after she arrived at the auction late and without her husband.
She joined the bidding but the house was about to sell for $155,000 to another bidder when, helped by daughter Tessa Williams, she made what became the last bid.
"It's lucky I did bring my chequebook," she said.
The building of a transportable three-bedroom home, finished to soft furnishings stage, was a joint project between Certified Builders and Mitre 10 Mega.
It was built in the Leviathan Hotel car park over the past month.
Mrs Williams plans to have the home moved to family land at Waldronville for her daughter and her family to live in.
Otago Community Hospice funding and marketing co-ordinator Lyn Chapman said she was delighted at "such a community effort put into this house.
"We are very grateful to everyone."
About 50 people attended the auction, which was conducted by Wayne Graham.
