That is not an absolute truth. The shootings could have commenced in a number of ways - we don´t know how. She might have been mulling over her next move, hesitating, then suddenly acting.
Claiming she went and got the moderator out to kill them in their sleep then couldn't go through with the plan and instead went around acting crazy which enabled Nevill to go make a call and then she caught him and merely hung up the phone then took it off the hook and marched him upstairs to shoot him in the bedroom with June makes no sense at all.
Either she was crazy and grabbed a wepaon of opportunity or she carried out a planned attack you can't have it both ways. Jeremy's claim he received a call that she grabbed the gun and was crazy along with his story of how he left the gun out painted his lawyers into a corner of what they could reasonably suggest occurred.
I realize Jeremy's supporters are so biased they will accept anything no matter how absurd in order to avoid facing his guilt but his lawyers had to argue before a jury and convince a jury. The jury heard his own words about Nevill calling to say she grabbed the gun and had gone crazy and his own claims of the state he supposedly left the weapon in. That created a conflict because he framed is as her going crazy and grabbing a weapon of opportunity but the prosecution's evidence related to the silencer being used meant that the best defense would have been to argue a planned killing but his own statements inhibited them from successfully making that argument.