Julia is part of MerseyGirls (previously Just Us) who had said they hoped winning Britain's Got Talent would fund pioneering surgery.
MerseyGirls are a five piece dance troupe from The Wirral, made up of best friends Alice (17), Poppy (14), Julia (15), Annie (17) and Rebecca (16).
Speaking to panel before their first audition, Julia revealed she has Scoliosis which would leave her unable to dance.
"This is my last chance and I've always wanted to do it," she said.
MerseyGirls went on to perform to Rachel Platten's Fight Song.
After the routine, a teary Alesha Dixon said: "I have so much admiration for you girls right now, I can't tell you. Seeing how you come together, when you're passionate about something I can't imagine not being able to ever do that again.
"I really couldn't and that's why we all live, for the things we love to do. It really touched me."
She then hit the golden buzzer to send the group straight into the live shows, where they performed this week and went on to make the final on Saturday.
Now Simon has said he'll fund a life changing op for Julia that will allow her to keep dancing.
"There’s no way I would ever have her [Julia] on this show and say, it’s all just about winning the £250,000. I couldn’t do that. You would do the same thing," he explained.
Speaking to The Sun newspaper, Simon went on: “You get letters, you get calls. You have to draw the line at a certain point. But I think if someone comes on in this situation, to do nothing would be, well, I couldn’t look at myself in the mirror.
“You create a connection. And I think with us, in this particular case, I think there is something we can do.
“There’s no way I would ever say: ‘Right, you came second, so it’s all over’.”
MerseyGirls will be performing live in Saturday's final on ITV from 7:30PM.
They're one of eleven acts hoping to win the show, which comes with a spot on the Royal Variety Performance and a £250,000 cash prize.