Eva was born with a hole in her diaphragm, which meant her organs were pushing up towards the heart and lung cavity stopping her lungs forming properly.
She has complete gastrointestinal failure and has to be fed through a tube.
Her condition has meant that for five years she and Tiff have stayed at the house while older sister Mela, 7, and dad Joel stayed at their home in Warkworth.
Mela has also spent a lot of time at the house - something her mum says has been a blessing for both her daughters.
"It's kept them together. They've been able to grow up together and be best friends and still see each other regularly.
"When I've told Mela off about something, she'll run out of the room and have about 10 aunties come and give her a cuddle and tell her everything's okay."
This week, "Smile Stickers" went on sale at McDonald's restaurants around the country to raise money for the Ronald McDonald House Charity.
Today is McHappy Day - when $1 from every Big Mac and Happy meal sold today will go towards the maintaining of the houses in Auckland, Wellington and Christchurch.
The Mitchell family have since moved out of the Ronald McDonald House into a small residence near the hospital, as doctors have told them they can do nothing more for Eva.
Ms Mitchell praised McDonald's fundraising initiative, saying the money raised would continue to help families who had gone through the struggles of having a sick child.
"At the end of the day, Eva's organs don't work ... I'm just happy to be able to finally take her home and just have a somewhat more normal life with her," Ms Mitchell said.
"She's such a happy little girl and it's something I've really wanted to give her for a long time. But we still go to Ronald McDonald House for our cuddles and pick me-ups.
"That's the kind of place it is for us."
*For more information or to make a donation visit: www.mchappyday.co.nz.
