The final touch for this costume was the crown, which Lady Macbeth is shown raising above her head in the Sargent painting.

That being said, the internet assures me that 1) this was supposed to be King Duncan’s crown, not hers, and 2) she never actually struck this pose in any of her performances of the play. But it’s still the most recognizable pose, so I had to make a crown to carry– and also to wear, since I wasn’t about to just carry it around all night.
Since I am not experienced in metalwork, I had three options: First, have a metal crown custom-made for me. That seemed awfully expensive for a prop. Second, make a fake metal crown out of craft foam and gold paint. That was definitely something I considered, but ultimately I wanted it to look really shiny and polished both inside and out, and I wasn’t confident I could do that in the time allotted. So I went with my last option, which was to find a reasonably decent-looking crown online and go with it.
