Maybe you should cover her up a bit; with a gag and ties for example!

You make your way through the crowd, and think a little. As you watch her squirm you figure maybe you should be nice to her and cover her up a little. Perhaps a gag and some restraints. Those technically count, right? They do cover a bit of skin.

You no longer have her own underwear with you to use however, that's left behind in the market square for some fortunate to find. You then look around; there's a small crowd now, cheering, jeering and whistling. Passerbys surround the unfortunate knight at a small distance, and shopkeepers look on from their stands, or stand on their tables or furniture for a better view. There's plenty here to work with! She doesn't necessarily have to be tied up with her own underwear for it to be embarrassing.