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(I wondered if she cinched those trekking chair straps tighter/closer, so it was more of a "V" shape than an "L," and then maybe tucked her pack underneath, perhaps that would provide the padded knee-propping effect?)
Could something like this set-up (lightweight inflatable mattress & lightweight frame) get you part-way to a solution?
https://www.thermarest.com/seating/chair-kits/trekker-chair/trekker-chair.html
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