I don't think the move by Cass was so terrible. She may appear to be at the bottom of the six person alliance on the other tribe, but Tony and LJ just put targets on their backs by revealing idols that they had. Their moves during tribal council also showed how closely aligned they are. I could see Cass, Trish and and Jefra (maybe even Woo) eventually teaming up to take out Tony and LJ. Those two become much bigger threats as the game goes on.
If the new alliance of six is able to boot out Spencer and Latasha over the next couple of weeks, Cass will have no original alliance members and will not be viewed as a threat by the other tribe members. At that point, they will probably feel confident in their numbers and start picking off "alpha males".
Also...
I really enjoyed seeing Sarah getting completely blindsided after declaring herself "president" earlier in the episode.
I know most people think the flip by Cass was not a "smart move", but I thought Tony, by far, made the dumbest decisions during tribal council. First he announces that he has an idol, then he shows it to everybody, and then has Jeff "validate" it. He could have kept quiet and used the idol on himself instead of allowing the other players to switch who they were going to vote for once they realized who had the idol.