Transitioning from Grace, mother of one, into Fairy Grace, the magical creature, requires a pre-party preparation which begins in the car on the way to the job.
"There are a few things I need to do mentally to prepare. I think about the little girl or the little boy whose party it is and I try and engage with what the mother's already told me about their child.
"I have to start the voice in the car before I get to the party because [adopting a higher pitch] you've got to talk in a very high pitched voice like this, you can't go in with a normal voice," she said, laughing.
The key to the illusion is making sure the children don't see her in her normal garb, which means parking around the corner from the house, putting her wings on out of sight of the party. When Ms McMillan-Caires arrives as Fairy Grace, the response is immediate.
"They are over the moon and they don't really know what to do with themselves. They either squeal with excitement or they stop in silence and are stunned."
That reaction is the best part of the job, she said. "[To see] their little faces smiling ..."
Ms McMillan-Caires said she wants to keep performing as long as she can, but running the business has already meant she's had to scale back her party appearances.
"It's exhausting but I don't want to leave it, not yet. I don't think I look too old yet.
"I'll keep going for as long I can get away with it, which I guess is forever - I can turn into fairy godmother when I get too old."
