I was never confident enough with CK to get that one working, but if you're looking for an alternative, TheL0neW0nder made a mod that adds 4 fully voiced companions with lip synced dialogue from New Vegas, including Cass, as well as Veronica, Raul and Arcade Gannon.
Here's the link if you're interested.
https://www.nexusmods.com/fallout4/mods/56994