oh wow, an author not shying away from the death penalty, and not dragging out the story, was fully expecting her to be around another 50 chapters or so
the death penalty is realistic for an aristocracy period, which seems like what this series is roughly set in, despite being a fantasy land
also, keep in mind she did try to more or less indirectly kill the duchess by sending her to a death area so if she gets killed instead it's hardly possible to complain or shred tears.
you may argue whether she deserved a death penalty or not based on your sense of values, but that's a slightly different matter than the two points i (and others have raised)
the maid's frustration, sabotage and jealousy is actually very believable, and from her point of view (or anyone's) there is no way she'd think the pushover duchess could suddenly become a competent modern office lady overnight and achieve everything she did.
Props to the author for handling it very well.
the other servants complicit in the story got off too easily, if there were any bad points in the writing.