Nikola Doak, from Motherwell, met the former Westlife singer after shedding more than six stone. She slimmed down from 17st 4lb to 11st 1lb after joining the Motherwell Slimming World group in March 2012.
Brian said: "What she's done is nothing short of incredible.
"Nikola is proof of that, by making changes to her eating habits and getting active, she's obviously completely changed her life."
Nikola was just one of 58 women from across the UK and Ireland to reach the Slimming World's Woman of the Year finals.
She said: "I'd tried losing weight before but I always failed miserably. Slimming World was completely different to anything I'd known before."
The overall winner of Slimming World's Woman of the Year will be announced next month.