3 yo girl "engineer" toy suggestions

I am looking for suggestions for my DD who will turn 3 in October. She loves all the girly things, babies, dressing up, her little kitchen, but also has really good fine motor skills and an "engineering" type bent. One of her first big questions was "How that work?"

So does anyone have suggestions for toys/gift for her? We have the Duplo and regular size Legos, an oversized Magnetix set, things that are a little like that, but are there other things that might take her to the 3-3 1/2 old level? I'd also appreciate suggestions on books that are good for her age on explaining how things work (because Mom doesn't always know!! :)

Thank you!

Wendy