"Zij is zijn persoonlijke secretaresse op maandag."
Translation:She is his personal secretary on Monday.
Yes, I have the same question. It might be useful if a Dutch native speaker could clarify what the original sentence means -- every 'maandag' or a specific 'maandag'. If it means "iedere maandag" (which I'm guessing it does) then the English translation should read: '...........secretary on Mondays.'