That receptionist at the adventure guild should be fired for not explaining things properly.
Translator here!
The receptionist says the only openings are
給仕 (kyūji) jobs, basically serving/waitstaff work, and then adds
どれも夜の仕事ですし, literally “they’re all night work/jobs.”
The important part is Setsu’s internal response. She changes that into
夜勤のウェイトレスさん? essentially, “A waitress working the night shift?”
夜の仕事 and
夜勤 are not the same expression.
夜勤 specifically means an ordinary “night shift,” while
夜の仕事 is broader and carries a nightlife-work implication. So Setsu interpreted what the receptionist said in the most innocent, literal way possible.
p11:
That seems to be a pretty standard euphemism, yeah? In that same panel, there is internal dialogue of "Night shift?" indicating Setsu was unsure about something, but does not try to clarify. I think the receptionist explained it well enough in-universe. The problem is a mismatch of understanding: Setsu can "hear" the words, but she doesn't necessarily "understand" them due to background, other world, etc.
There's other scenes where Setsu sees something, but it doesn't trigger as a flag for her.
You pretty much got the right idea overall. The mismatches in understanding are present throughout the chapter in the original Japanese: Setsu hears what she’s being told, but misses all the implications.
I tried to preserve that in English without translating everything too literally. So...
“waitstaff” and
“night jobs” were chosen to keep the same ambiguity in English.