You think she's making too much noise

She screams and yelps at you, telling you to return her clothes. The squeels of embarrassments are music to your ears, but although you savour the underlying humiliation you find her shouting to be a bit too loud. It's unbecoming of a knight, especially a naked one who should think twice before drawing in people with her noise. You consider her demands for a second, figuring you can hit two birds with one stone, and select one of her pieces of clothing that should do the trick.

You walk up to her, an indistinguishable blur of activity follows, and voilà!

You've used her own garterbelt as a gag, using the straps to fasten it behind her head.

Her eyes widen with further embarrassment, and her face is red with shame. Her protests are muffled through the gag. You wonder what a humiliation it must be to be tied and gagged with your own underwear, but when you look at her face you get a pretty good idea of precisely how humiliating it is.