Take up her suggestion - to the servant's detriment

Just as the servant girl is about to close the door, you zip in and have a good go at her. She appears to be of a roughly similar age as lady Evellyn, and is wearing a white coif over her brown hair, an ankle-length gown with a bodice over it, and has an apron tied around her middle.

You go straight for the bodice first, unlacing it as per usual, and then untie the apron. Once those are taken off, you can easily slip off her gown entirely, and take her conservative undergarments away as well, leaving her in just her knee-high socks. She's certainly a bit chubbier than the fit, muscular knight, but while she might not have a toned stomach like her lady, the extra bit of fat primarily shows up on her major set of tits, now about to sag under their own weight. You let her keep the coif, and the apron too - she's gotta be able to finish her chores.

You grab her clothes in a bundle and find a good place on the inside of the yard to climb unto the wall, lie low to avoid detection, and get ready to watch. From on top of the garden wall you can see on your right the crowd mulling around some of the remaining naked women, and on the left the two girls, both now either naked or very nearly so. Motion resumes in the world, and upon feeling her disrobement the servant shrieks, and flails about searching in vain for her clothes, tits wobbling, before sinking down in a crouch and trying to cover her entire frontage with the small apron.

Remarkably non-plussed, owing to familiarity with your practices by now, lady Evellyn nudges the door shut, remarking "I did warn you".