How do I clarify to readers that the bolded dialogue question is a rhetorical question?

Two characters, Scythe Master and Claudia, are having a conversation in this book I'm translating. The first speaker is Scythe. (Bolded part is what I'm 87% sure is a rhetorical question, based on what comes before and after it's said.)

“Already arrangements to locate his immigration documents are underway, in addition to a method of erasure. Before long there will be no trace of him for anybody to pursue. The secrecy is flawless.”

“…I think that is agreeable. Scythe Master. I’ll leave this young man to you. However, Ein and Zwei…. Your students’ names at least, perhaps they should have been given a bit more thought?”

Saying as such over her shoulder, Claudia also leaves the room. At her back the silver-haired man scornfully laughs until she is out of sight.

A friend of mine suggested that I change Claudia's second line to

However, Ein and Zwei.... Perhaps your student's names should at least have been given a bit more thought.

I think this suggestion is due to the reader (my friend) not realizing that the question was rhetorical, as kiamlaluno states in their answer here, "...whoever asks the question is not interested in an answer, but wants to remind somebody else of something they should, or could do" (kiamlaluno).

How do I clarify to readers that the bolded dialogue question is a rhetorical question?

"Your students’ names at least, perhaps they should have been given a bit more thought?"

Saying as such over her shoulder, Claudia also leaves the room.

The fact that Claudia leaves the room, not expecting an answer, makes it obvious that it's rhetorical. The action speaks for itself, so you don't need to worry about the sentence in the first place.

If the action doesn't mark it as rhetorical, no amount of rephrasing is going to. (Unless you use a deliberate dialogue tag, like Claudia said rhetorically—but that would be a little forced.)

As for the rephrasing of the question, the suggested change is certainly not as nearly a rhetorical-seeming question as the original version. In fact, it reads more like a statement than a question.

Just using a question mark would fix that—although I still don't think it would be as good a sentence as the original. However, assuming I were to use such a rephrased version, I would make a slight change to the word order:

"Perhaps at least your students' names should have been given a bit more thought?"

(With the question mark at the end.)