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
I have a couple smart nieces. One of them did want LEGO — she wanted a whole LEGO-themed party. I was the only one who bought her an actual LEGO set, not one of the ones aimed specifically at girls (LEGO and Friends, IIRC). Yeah, guess whose she wanted to actually build — and guess who she recruited for help doing it, while all the other sets sat in boxes (dunno if they were ever opened).
Beyond that, I stuck to the “edutainment” aisle. Science-y stuff. Books are another good option, if you can find a fantasy series with light romance (but nothing erotic, obviously). That’s more for older girls though, a six-year-old probably can’t read. That being said, audiobooks are a thing, and if they’re a tablet kid, an Audible/similar gift code might not be a bad idea. They can do a lot worse for themselves with a tablet than having someone read to them.
Also, crafting stuff. Crochet kit, beads, anything that lets her “make” something.
to add to the DIY section of your comment - air dry clay, a set of basic clay working tools, and a set of acrylic paints (+ varnish for the acrylics) could be very fun. cheap air dry clay is cheap (i’ve seen 1kg go for ~$3), a basic set of tools and paints also won’t break the bank, and it’s absolutely amazing fun!
even with 0 skill you can make nifty things - like minature foods (a blob? potato. cylinder? cucumber. ball? so many options here), simple figurines, animals, accessories for other things, candle holders - bascially, the only limit is your imagination.
though if you do think that’d be a good idea one word of warning - air dry clay is not food safe, any cups, plates, or dishes made with it can only ever be decorational. (the only clay you can eat off is the kind that you need to fire, glaze, and fire again at +900°C)