On Instagram, Maddi shared her joy about the encounter, describing it as “one of the best days of my life”.
“Thank you for being so kind, for making time for me, and for giving me a memory I’ll never forget,” she wrote to the singer in her post.
The charity football match is set to take place at Maldon and Tiptree’s ground on Saturday, and will see a team of celebrity players face off against a team of bodybuilders from a gym where Maddi trains in Witham.
The Maddi Foundation said its aim was to raise £2.5m to fund research into SPG15, a progressive neurological disease.
It is caused by a genetic mutation and symptoms include learning difficulties, involuntary movements and dementia as well as muscle movement and pain.