Symbolism, Imagery, Allegory
Katsa has five rooms in Randa's palace: one for sleeping, one for eating, one for bathing, one for sitting, and one for working—and by working we mean embroidering, crocheting, sewing, and darning. (That last one means mending, as in darning socks, by the way. Not sitting around and thinking about things that make you say darn.) These are the types of work the room is supposed to be for, and if Katsa were a more typical lady of the court, these are probably the kinds of things it would be used for.
But Katsa is not a typical lady of the court, so instead of weaving tapestries or making lace doilies, Katsa uses her workroom as a place to store her weapons and hold Council meetings.
Instead of cross-stitched family crests or crocheted quilts decorating the walls, Katsa has bows, staffs, and swords; instead of needles for sewing and mending, Katsa's workroom contains an array of knives and daggers; and instead of a spinning wheel or a small desk where she could practice calligraphy or illumination, Katsa has, as the centerpiece of her workroom, a "solid, square table," where the members of the Council meet to discuss strategies and plan missions.
Get the symbolism here? While Katsa has allowed Helda free reign in the decoration of her bedroom and sitting room—the bedroom "because Katsa […] refused to form an opinion on it" (9.58), and the sitting room because Katsa never uses it—she has maintained control over the design of the one room intended specifically for feminine use. And she's completely subverted its intended purposes. Just as Katsa herself, by making the choices she makes and doing the things she does, has subverted her typical gender role.