My brother does metal work, so he made his (WHORE) gf a rose out of metal. Idk if you can apply the same technique(use your hobby or skill to make her something to express your love). It's a cheap way to tell her you love her.
It your hobby is hardware\software engineering then forget the first idea. IMHO Women hate technology.
They just want to know you care. Don't get her something stupid, like a soccer ball, lol.