Helen, I agree in general BUT when the girls sign on, they've "declared" they're fit just like we have; no decision is generally required to be made by the capt.
Yes, if they subsequently inform the capt they're unfit, they should be stood down but any good purser should already be headed down that path by the time the capt hears about it.
On the other hand, you might not even hear about it. The purser often takes care of it, just as Billy-Bob has pointed out.
And don't expect any EK management to stand in the way of the law when it bears down on you....
Amen brother. (Or sister??)