Looks like a Job for a Maid! The Tales of a Dismissed Supermaid (Manga) Volume 4

Nina and her friends are driven to the Yupiter Empire in pursuit of two lupalune mercenaries who might be Tien’s parents. But their only lead turns out to be a dead end. When the pair of warriors are so popular that Maid & Co. are turned away at the gate, Nina, determined to help Tien no matter the cost, takes matters into her own hands. Ignoring the warnings of the others, she infiltrates the mercenary estate as...a maid! But not all is as it seems in the Dark Frost Mercenaries’ mansion. Uncovering the mysterious mercenaries' secrets may be a task too big for even a supermaid to handle!