Nona doesn't knit the entire ribbing combined, just the one purl stitch right after a knit stitch - She uses it to tighten up that particular knit stitch which sits right next to a purl stitch. Yes, the combined purl stitch is twisted which is why when you encounter it going back the next way, when it will be facing you as a knit stitch, you knit it through the back loop so that it sits properly and then you purl the stitch immediately after that in the combined way to tighten up the knit stitch you just made.
I'm a boy, by the way.
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