It seems that even in the 9th... But that's not the point. Yeah, I think it will be Jules, but not because she is the “remote control carrier” (after all, this has not been confirmed and is only my assumption), but because, imo, she is in the most vulnerable position among all the sisters (as strange as it may sound to some).
So I can assume that if the likely attempt to kill a sister is part of Alessandra's evil plan to get rid of two sisters at once (although we haven't been told which ones), then Jules will be the "weak link". Veronica poses no threat to Alessa's plans (oh, if only we knew for sure what those plans are and whether she really wants to be the gray cardinal behind the one who is formally in power, or whether she actually wants to concentrate all power in her own hands)...
But Dominique poses no less of a threat to her than Jules, since Domi openly claims sole power and did not even offer Jules an equal partnership, appointing her as Her Majesty's court jester, who is simply allowed (away from the respectable and honourable ladies) to indulge in her sadistic perversions with murders and other things. And the next Alessa's attempt (if it happens at all) could be the organization of Domi's murder.