I have been able to get Cass to be my Follower by completing the initial Crimson Caravan Mission and doing the mission where I clear the road. As soon as I speak to her she calls me [censored] hole and tells me I need to change my attitude. The next time I speak to her she tells me that she is not going to follow me any more and ultimately leaves. Even if I speak to her after I have completed many of the Crimson Caravan Missions, I get the same response. I believe I have explored all the dialog options and still can't find a way to progress her mission.

Surely this must be a bug? Has anyone else experienced this? Any help?

It's most likely due to your standing with a faction she is for. I would check your faction status, and see who your villainous with.

I wonder if it has to do with you completing CC quests before ever talking to her. I talked to her long before I went to CC. In fact, she gave me the quest to go there to begin with. If you can, revert to a save before you did any CC quests and see if it works. If it does please update us so it can be looked at by developers.

I started the CC quest when she gave it to me. Does anyone know which fraction she supports/ favours? I'm gonna check when I get home.

I'm approximately 25 hours into the game. My fraction stats are:
Goodsprings - Idolized
Great Khans - Neutral
NCR - Accepted
Powder Gangers - Vilified
The Strip - Neutral

It appears that I can only speck to her twice because she warns me twice to change my attitude then leaves. Just checked my Reputation which is Evil, maybe that could be the problem.

Maybe there are concequences to being an ass in this game. Worse thing is I dind't even realise I was that bad. I will try to improve my Repuation and update this thread.

I'm pretty sure I know why.... I currently have her as a companion and without giving too much away, I'd say doing CC quests is what caused the problem. There's a certain somebody she wants dead, so it's a bit of a conflict of interest

I've sent Cass back to the Lucky 38 and will try to talk to her if/ when I'm good. Won't hold my breath though because I've got Veronica as a follower.

u need to do the crimson caravan quest to get cass,u need barter level of 50.tell her u wont to buy her out for 600 caps.shell join u then.go back to crimson caravan.quest complete..