Hope she enjoys her day there - having been there recently myself for another competition i can simply say it will be an experience that will be with her for ages - whether she gets the title or not.
As you say "she is already a winner" - in my eyes too. Everyone in my eyes who walks through those doors (of a Slimming World group) and makes the commitment to change their life is a winner - even more so the younger ones as they will be learning lessons now that i can only wish i learnt when i was their age.
Good luck to her - and all the other attendees next week.