It's about the only way those girls will get enough, and only when Ainz straight orders them to do it. It's probably her day off in rotation, so she's still in her uniform just in case Lord Ainz needs her, but she's resting per his orders. One does not defy the orders of a Supreme Being.
I'm not sure why, either because Limbus fans like yuri or Signalis fans like Gacha, but there seems to be a strange amount of overlap between the 2 fanbases.
Took me a few confused moments wondering if this was a sequel to some Seija+Kutaka book I hadn't seen, but I think they're actually talking about how Seija and Shinmyoumaru came from the world of oni in the DDC backstory.