My spontaneous theory:
The CD which forcefully married Ginny really felt in love with her. He was kinda building a real relationship here, which made some other CDs, or even the Gorosei, worrying, since a child or smth would ruin the hierarchy and the strict separations of the races. Maybe Ginny was even a D..
Following this, they started to poisining Ginny, like they did before with the village of Law and his family, with Amber Lead. Maybe this is one of the powers of a Gorosei, maybe even Saturn himself.
With that, they convinced her Husband, the CD, to get rid of her, before she is infecting the CDs too. It wouldnt surprise me if the husband himself died too.
Also, my theory a long time ago, was that Luffy is also a mix of CD and D., which is what the Gorosei heavily try to avoid. Maybe this is some requirement for awaking Nika or smth.