When I want a quote ... I start googling ... a gazillion will come up!
Sometimes one that works ... sometimes they give me inspiration of what I want to say.
The religious slant was suggested ... though a child might appreciate something connected with one of her favourite nursery/Disney characters etc.
When you don't know the child or her family, I'd opt to keeping it very simple and away from anything too personal .... something like "Cheering you on, (name)"