I'd buy her a book on a random topic that goes in depth, while maintaining age level. I got a lot more of a kick out of depth than breadth when I was a kid.

Technics lego are… well, I never made anything out of them that really took advantage of the mechanical elements, mainly because I didn't have the motor. Making a car that runs if you turn a wheel… well, you need to track it, and then you're basically pushing it along.