I've been reading about the case since it happened, and it's my understanding from the autopsy findings that the girls were smothered/suffocated before they were placed in the oil tanks. CW has changed his story multiple times, so it's not really clear if they were killed at the house, or at the oil field. They were so small, I just can't imagine their fear, their father...so horrible. It's overwhelming to me. Chris Watts is a monster.
In terms of SW and her social media presence...it seems clear to me, that it had a negative impact on their family/marriage. That being said, her LACK of social media activity the morning she was killed, alerted her friends that something was very very wrong. He should have used her phone, as her, to respond to her friends. But he wasn't smart enough to do that. If her friend Nickole had not shown up at her house, I have to wonder, what would have CW done with her car, her phone etc