Saga Star Wars character flaws

This is partly addressed by the movie: "the Queen's wardrobe, maybe, but not enough for you to barter with. Not in the amounts you're talking about."

Okay, so "the amounts you're talking about" were for the price of a hyperdrive. How much is a slave compared to that? We don't know, except that they're worth at least the price of a podracer. But it's not too hard to imagine that the Queen's wardrobe wouldn't have been enough to free Shmi.

 

I very much doubt Amidala owned any of her regal wardrobe. Especially since on Naboo it's an elected position. The wardrobe is probably owned by the state of Naboo.

Probably Qui-Gon/Obi-Wan forgot. Must be the heat of twin suns.