Soft Shell Crab
I know this is a long shot, but in order to satisfy a pregnant woman's craving, is it possible to find fresh soft shelled crab in Paris?
I would look in two directions, first try the best fishmonger you know (I used to like Poissonnerie du Bac, 69 Rue du Bac, 7eme). If they can't help head out to the 13eme to see if any of the Asian fishmongers/supermarkets have them (given their use in Asian cuisine), you may find they are in the freezer section though.
Late May should be the season. I would also inquire at the 'hood poissonnerie, whichever 'hood the pregnant lady is. Even if one does not see the crab in the aquarium, I would think one could order it.