Dungeon Kurashi no Moto Yuusha - Vol. 4 Ch. 27 - What’s Nina feeling before the moment of truth…?

[MangaDex]

 

[Kaarme]

To be honest, it's difficult to see the point of the whole group, including the empress, joining this rescue mission. Everyone in the empire ought to know the empress loves her daughter and gets along with her, so her presence would make anyone suspect she won't simply allow the princess to be taken away (and murdered). After the empress herself disappeared, the local lord ought to be highly suspicious, but when the empress returned, he should be thrice more suspicious and quite certain any rescue mission is going to happen right then and there. We saw previously the lord was quite careless before, so a sneak attack with no forewarning should have been better.

One might think the rationale behind their choice was the expectation the lord would be on high alert after the empress disappeared, but nothing suggests anything of that sort. The empress behaved as if nothing much happened and has been since free to do whatever she wants, including having her knights wander around.