Here's what Bill said about what he thinks they might be planning for Ginny.

'One: Ginny could be put up for a show trial, maybe even publicly killed, as a warning example to anyone else thinking of resisting them.

Two, she can be kept as an unwilling hostage, and they'll use the fact that they have her in their clutches to influence our movements or decisions.

Or three, she can be kept as a hostage but presented as someone who's seen the light and returned to the pureblood fold, ostensibly joining them willingly. I don't think that we can discount that third possibility, as it would obviously suit Bella's purposes beautifully and at the same time be a huge blow to us. We know perfectly well that they have no scruples whatsoever about lying the press.'

I can't imagine it's the second. It wouldn't work and Bellatrix knows it.

I doubt it's the first because they've never bothered much with trials. We care about looking fare and just. Why would they start now?

I think it's probably the third. They're going to make her pretend she's seen the light and returned to the pureblood fold.