Newborns

So last night I was thinking about the Bree Tanner book. It says that Riley was made a year ago. Bree three months ago. So that would mean that right after James was killed that Victoria made Riley. How soon do you think she did this? And when do you think she starting making the plan to make an Army to go after the Cullens? And last do you think Stephanie had this planned the whole time or just came up with it when she was writing Eclipse?