Yes, it is my one beauty indulgence, and my almost 11 yo loves polish, too.
I paint my toe nails in bolder colours (maroon, dark blue, purple) and my fingernails in nudes, pinks, or pale frosted colours. But sometimes, I paint my ring fingers in a contrasting shade for accent.
I can't do nail art well enough. For my dd, I do polka dots, or put some glitter on her nails. And once I block-painted the Ravenclaw colours on her nails.
I use OPI polish because I love the wide brush. CND is also a good brand.
Tell your dd to sign up on pinterest. There are a ton of ideas, step-by-step with photos.