All this mobile phone stuff is screaming 'pre-meditation' on both their behalves (to me). Sarah never went into shock about Scott killing B, she went straight into the texting, gmail, Insta stuff....because she knew why Scott went out and that B wasn't coming back alive. The 9 minute phone call was more to say that the job's done, not to say "Oh my God I got so angry with her and got carried away, I'm so sorry, please forgive me as I truly didn't mean it to go that far". The latter would have left Sarah in too much shock to start the cover-up stuff immediately, but with the former that phone call confirmation means it's time to get covering up before they have to report B 'missing' to the police. All JMO.