Man, I always hunt for this exact vibe! So many steampunk stories have the princess just wearing the gear, not making it. One standout is 'The Iron Duke' by Meljean Brook – Lady Yasmeen isn't a princess by title, but she's a sky captain and airship engineer who absolutely rules her world. She’s constantly tinkering with her ship’s engines and weaponry, and her technical know-how is central to surviving political schemes.
Another is 'The Clockwork Crown' by Beth Cato, where Octavia Leander, a medician who uses gear-driven devices for healing, invents new apparatuses under pressure. It’s less about crowns and more about using invention to subvert a rigid system, which feels princess-adjacent in spirit. Sometimes the best 'princess' inventors are the ones dismantling the throne itself with a wrench.