Luckily for Dame Simonetta
the puffball is an immature specimen. The flesh is spongy, like a dense loaf of white bread. Presumably as these puffballs eventually mature, the outer skin will become brown and leathery, the inside will darken and turn into powdery spores, and a "belly button" will appear on top.
She is able to withdraw her sword without incident.
Here is a cross-section of a firm-fleshed young puffball, in its edible stage:
And a mature specimen ejecting its spores: