I recruited Veronica before Cass. And I did many of Veronica's quests along with all of the Brotherhood's quests (allowing Hardin to take over as Elder) and becoming a Paladin by killing the Van Graffs.

Then I took Cass around to investigate her Caravans and it turns out she wants to expose / kill the Van Graffs and Crimson Caravans.
I don't mind having killed the Van Graffs, but the Caravans seem legit enough and I was doing their quests -- also I don't care to ruin my rep with the NCR by wiping out the Crimson Caravans (And I am doing quests for them at he moment).

But because I killed the Van Graffs previously, I am unable to take the option to report their deeds to the NCR because Cass gets cross with me for 'changing my mind' and having killed the [censored] anyway.
Then the only option is to wipe out the Crimson Caravans.

This isn't the only example of overlapping quests. What's the point of this? So, I can't resolve Cassidy's personal quest without resorting to murdering everyone in the Crimson Caravan?