They're going to have to have a very good explanation why she's suddenly pro-horde, trusts Sylvannas, and is engaging in necromancy. Especially since Sylvannas cursed Lillian to undeath to be a weapon in the first place. Every quest with her is either neutral or telling the forsaken to piss off.
The point is that Voss has other communities to join if she wants one. It's coercion to tell her that she has nowhere to go except the Forsaken, knowing that new undead have little choice to begin with.Tess was also very nicely at home in the rogue hall, but I wouldn't believe for a second she's not Alliance.