Ms Cooper lives with her partner of 20 years and their two children, Byron, 11, and Zara, 6.
"I don't think the kids really comprehend what has happened, they just know mum and dad have been crazy since yesterday. I've never owned a home, I've never even looked into it because it's been such an unreal possibility.
"I work hard and we've struggled, we rent a home and have a car that's just about dying so the timing couldn't have worked better," Ms Cooper said.
The store manager of Masterton Countdown delivered her a letter advising her of her win last Thursday .
"It took a long while to get through. We actually googled what the promotion was and didn't believe what I'd won. It's been crazy, we've been walking around all day at home today on cloud nine, it's just so unbelievable, I keep looking at the letter," Ms Cooper said.
She said she had forgotten she had even entered the competition.
"I didn't consciously think that I might win that. I didn't even think of the competition, I knew it was one but I didn't go out to enter into it."
Ms Cooper said she would meet Countdown staff to go over the finer details next week and that the family would probably take a trip to Queenstown to look at the house, which is still being built.
"It's in a really beautiful area, it's right off the Shotover and you can see the Remarkables. It's a really beautiful modern show home."
She said she was unsure whether the family would make the move to Queenstown.
"We've never thought of moving out of town so we're not quite sure what we're going to do, I just know it's going to be awesome.
"I work locally and I really, really love my job so I wouldn't want to leave," she said.
Ms Cooper is the co-ordinator and facilitator for the Wairarapa Women's Refuge Tamariki programme, a programme for children who have lived with, or experienced family violence.
She said she might enter more competitions in future.
"You've gotta be in to win."
But she hopes others will be able to share her good fortune.
"I think this is such a once-in-a-lifetime gift that I'd never see that happening again and I wouldn't want that to happen to me again, I'd want someone else to experience what we are right now."