Would prefer it to not be “hair” 'makeup" girlish oriented, but rather something challenging for her mind. I am her Uncle, and would like something maybe aimed at DIY outside of Lego if you know what I mean. Budget is small, maybe 39.99? Can move either way if needed
Advice, much needed as a 36 y/o male with no kids
Maybe not in the “smart mind challenging” category but there are plenty of craft kits for your budget: paint canvases by numbers, make your own accessories with clay, bead jewelry, basic engineering kits (build your own robot types), dig your own fossil kits, build-this-or-that-with-LEDlights, gardening kits for kids, etc.
My point is to expand your horizon a bit, it’s perfectly fine that you want to cater to her intelligence and not just go for something girly in a cliche sense. But she can also enjoy crafting stuff.