Jin finds Rousseau's camp, she shoots Robert

After the time skip, Jin sees smoke coming from the beach and goes to investigate. He finds Danielle Rousseau's camp. He finds her music box with the dancers that Sayid fixed for her in season 1. Jin also examines her shelter which has a box of explosives next to it, meaning she must have already been to the Black Rock. After noticing flies buzzing around, Jin finds the bodies of Brennan and Lacombe who have been shot. He hears Danielle and Robert arguing and goes to see what's happening. He finds Danielle holding a gun on Robert and she says that the monster changed him. Robert says it's not a monster, "it's a security system guarding that temple." He convinces her to lower her weapon but as soon as she does he tries to shoot her but the gun doesn't fire. She then shoots Robert in the head and sees Jin and starts firing at him. As he runs away through the jungle, time skips again.

So what happened to Robert down under the temple with the monster to make him turn on Danielle? Is Robert right about the monster being a security system for the temple? It would definitely seem that Danielle isn't as crazy as she initially seemed in the first few seasons.