Today’s picture is of St Elizabeth spinning in a woodcut from 1511. There are a few St Elizabeth’s, but I think she might be St Elizabeth of Hungary whose charitable pratices included spinning wool for the poor.
© The Trustees of the British Museum
What I love about this picture is that you can see spinning in various stages in the one image.
This women here is holding her spindle how I do when I’m first drfafting out a thread across my body.
This woman looks like she is suspending her spindle after drafting it out to add more twist. She even appears to be putting her thread over the back of her spindle hand the same way I do.
There is a little basket of spindles with th whorls removed holding spin thread in the foreground.
15thcenturyspinning 
This image has interesting parallels with mythic representations of the Norns and the Fates: a crone, a matron, and a maiden spinning the threads of life.
I think the image of the woman drafting across her body is one of the most convincing ones you’ve found to date.
(P.S. To strengthen your argument for this style of spinning in medieval Europe, have you considered trying to prove the opposite is true – that cultures that spin vertically and suspended drew women spinning that way. You could look for extant ancient Greek spindle whorls, to see if they are larger and broader and thus would spin for longer than a medieval one, or compare Pre-Raphaelite art with photographs of spinners from the same era to see if the artists’ notion of how spinning was done influenced how they painted medieval-esque women spinning.)