Video report by ITV News Scotland Correspondent Peter Smith
She's going through chemotherapy for a rare form of leukaemia, her dad Scott had to keep going to work during lockdown.
The family made the difficult decision that he would move out to protect his daughter from the risk of infection.
That was seven weeks ago.
In that time, he would come back to the house every day and stand in the garden just to see Mila's smile.
They spoke through a slightly open door, but that was as close as they could get. Until today.
Scott has stopped working now, having been furloughed by his employers.
That allowed him to go into a period of isolation, and today he was given the all-clear to move back home.
But he hadn't told Mila. Today, the four-year-old thought her dad was just coming to the garden for a catch up as normal.
Then came the surprise.
As soon as Scott walked through the door, Mila's face was a picture.
Watch the moment Mila is reunited with her dad:
We witnessed the emotion of that reunion. And how hard that time apart has been for the Sneddon family.
Without her dad, it's been down to Mila's mum Lynda to take the little girl for each session of chemotherapy. Mila lost her hair and her immune system.
There were tears, there were tantrums, and there was despair at the cruelty of it all.
During lockdown, Lynda also lost her grandmother who tested positive for coronavirus.
It has been a tough time. And today's moment of sheer joy has been a long time coming.
When lockdown began, Mila's big message was for everybody to stay indoors.
The way she saw it, that would slow the virus and help her get her daddy back sooner.
Today, Mila's two favourite celebrities heard the family was reunited and sent an invitation for them to come and see a show when things get back to normal.
Mila could barely hold back the tears of joy.
Mila believes people listened to her before and that's why she has her family back together now.
Coronavirus: Everything you need to know