("Clerk" is far too broad in meaning, and in some contexts it suggests no real training or education at all, rendering the term a poor descriptor for someone who has completed Diplom-Kauffrau studies.)
[not meant as a dig, but answering the question]
I wouldn't have a clue, but this is not a good comparative illustration and is somewhat irrelevant. I wouldn't need to know, if I was gaining a Swiss qualification for a position in an English speaking company. Likewise for the OP's wife, she would be familiar with Swiss languages and English.
This was roughly the point to which I was eluding.
Explains a lot.
As far as I know, there is no official translation, but they should be able to help you out. It's even harder if you have BMS (Berufsmaturität), cause then you're able to study and should be translated as something a bit higher then only Kauffrau EFZ.
On the last page I found this document where they expleany what a Kaufmann/Kaufrau EFZ is; they translate it as "commercial employee". But depending on the "Typus" B, E, or M that may be a gross understatement. Anyway, I am surprised that this topic is not discussed in the Berufsschule.
The term 'graduate' in a UK context is totally misleading, as it would imply a University Degree.
It is one of those things that just does not translate well and needs an explanation. It's like saying what the the Swiss equivalent of 'Toad in the hole'! Best to leave it in the original language and explain what it is. Anyway the nearest equivalent will be totally different in UK, US. OZ, CN, etc.
As said above, the translation is not important, but the job/qualification is.
If it's a vocational school, I'd go with Administrative Assistant.
If it's a professional school, I'd go with something like Management Trainee.
Once my friend's son used the above on his resumé (not CV ) he started to have better responses to his applications.
His take was it that the magic words 'Swiss Federal Qualification' that prompted the reviewer to read further; without that, his resumés were being dismissed as unskilled. Remember, most HR folks will only read the first few lines before deciding to bin the resumé or not.
Of course, a listing of actual skills gained via the Kaufmann diploma/apprenticeship is critical as well. One needs to assume that a non-Swiss reviewer will have no understanding of the diploma, and one needs to spell out exactly what one has been trained to do.
(It's even more difficult in that a US-style resüme is should only be 1-2 pages. Good luck explaining a foreign education system in brief. )
Sending best wishes to your wife with the job search...
The best discription could be Business Administrator.
Since you think Clerk is too lowly or broad.
A clerk is not "lowly" but it isn't a full fledged manager or administrator either.
My wife is setting her CV up in a new layout so that she can use some of the descriptions of the apprenticeship instead of the "exact" title as there is no such thing.
So thanks again! you were a great help!