Thanks for the replies so far!

Yes, she is traveling from Moscow. Her visa application originally covered the 30th April but it seems a mistake was made and it came back starting beginning of May, so there's no way she would arrive in the country when the visa starts, only before...

By detention, I guess this means 'being held' within the airport until the valid start of the visa. Although not ideal we have discussed the idea of her continuing the rest of the journey from Germany by train or car, but would this require a different kind of visa? (hers is type C but issued by the Netherlands embassy). Obviously if her detention occurs in Germany she will miss the connecting flight.

I will post any more I hear about the embassy in case in future someone else gets into such a situation