Do you mean the conversation when she opens up? It happened at just wandering the Wastes for me when I wanted to give her some crap to carry, she launched into conversation. Maybe the line was when she explained what a fish was? That is my favorite line in the game and made Cass my Favorite companion. It's an Int check, but don't know if player six has any effect on it.
No, no.. this was something completely different. It was subtle, spoken quietly and sounded like an implied reaction to a pass or come-on from the courier and loaded with enuendo.
I had the volume down low and wasn't really paying attention so I missed some of it, until I realized what she was saying...
I only WISH I had the exact words, parts of it went something like: Others have tried to... but never manage to go deep enough to do any good. It would be really hard...
I even googled for a while trying to find where somebody had quoted it. Maybe one of the PC guys can G.E.C.K. it out of her somehow? (I have no idea if that is possible)
Please, somebody tell me that I didn't imagine the whole thing.