The consular diplomat is accused of visa fraud, i.e. lying about how little she paid her maid in order to get the maid a visa.

I would think that if a friendly country’s diplomat persists in misbehaving, you expel them as discreetly as possible (or, better, ask their government to recall them) with minimal disruption of diplomatic relations. At least two possibilities come to mind:

1. An appalling combination of thuggishness and incompetence toward a major ally.

2. The real reasons for the arrest have not been made public.