Garage Band is free with a Mac...
And Logic Pro is a cheap subscription or very fair price when somebody like her is ready to take the next step. Maybe they even have a nice uncle who'd like to pay for it?
Yes, but depending on what you put in front of your kids, they're going to get different experiences when doing things for fun and curiosity. So why not help them a little on the way with the right tools and right toys? They'll find a way to get into the weeds and explore their curiosity one way or the other - isn't it much better that they learn about music or audio producing, or photo editing, digital art, or 3D modeling, instead of learning about how to fix the Windows registry or change a configuration file?
A kid will make a spreadsheet about dinosaurs if they only get to play with an office computer. Parents can help them by giving them something better to play with.