My adult fantasy WIP is unfortunately stalled a bit at the moment, and I've set it aside for now. For ewhat it's worth, though, the strict <20 words pitch would be:
'A mythical machine can recreate the perfect world. The decision whether it should be used lies with a limbless thief.'
A longer pitch, but one that describes the core of the story better, might be:
'When a limbless thief finds a machine that can recreate the world in a perfect state, she must decide whether to sacrifice the person she’s fought so hard to be for the chance to regain who she once was.'
I can't find a way to shorten the latter much more than this (almost twice the suggested length at 39 words), but it does define the theme and the MC's journey far more accurately.