Maid and princess seem to be in hiding. The crash seems to hint that they were found and I guess the brother's life was threatened in exchange for the princess's life?
Why the princess wasn't just forcefully taken if the hiding spot was found instead of the maid having to cajole her to the gallows is beyond me lol
My guess is that by hiding the princess, the maid was marked as a class traitor, thus marked for death, but was given a chance to be absolved and save herself and her brother in the form of betraying the princess and publicly bringing the princess to the gallows.
That kind of shit did happened irl in China during their Cultural Revolution, even family members were made to throw each other under the bus. Xi Jin Ping himself was made to publicly denounce and cut ties with his own father, a senior member of the Communist party who was persecuted by the mobs, otherwise he would have been done in by the mobs too. And he did it, then kept his head down but still attached to the rest of the body, until he got the chance to moved up.