TIA Pugh's bone marrow transplant is set to go ahead today (Tuesday) after a week of tests and chemotherapy.
The three-year-old from Bath Road, Worcester, is battling two extremely rare diseases and will undergo the operation at Great North Children's Hospital, Newcastle.
Bone marrow was harvested from the anonymous donor, who is not from the UK, yesterday.
Her father Nick has been updating the Facebook page Tia Pugh Immune Deficiency during their stay writing yesterday: "Today the donor gets harvested for bone marrow and I personally would like to thank this person as it's giving Tia a chance in living.
"Without blood or bone marrow donors many people would have passed away and we would like to thank all the people who are on the register and donate blood regularly as Tia has had to have several blood transfusions in the last couple of years.
"This is a worldwide thank you to all the good people on the planet and the followers of Tia's page.
"Tia's BMT is tomorrow and we do feel scared but Tia is making us forget about worrying as she is very happy and smiling a lot."