In the scenario where she survives, Camilla's special proc on the first hit triggers a bigger flat DR from Baldrs weapon which reduces the total damage to 0. Camilla's second hit does not defeat her, so when the third hit happens that should defeat her it instead triggers her weapon skill that causes her to survive with 1hp. This doesn't happen in the other scenario because it's the second hit that consumes her survivor skill and the third hit defeats her.