What weird and wonderful tangents this hobby takes us off on!
The more I look at Minnie's "knees" ... the more it looks like a "cage" that was - and still is - often used (for example, in hospitals, for burns victims) to keep either the weight or the scratchiness of fabric, away from the lower legs. I wonder if Minnie had had some sort of injury, or a skin condition that made contact with the lower skirts of her dress either painful or irritating when she sat down?
*ps it's too early in the morning for me to even think about counting pleats LOL*