This is complete speculation on my part based on the bits and pieces of interviews I’ve seen from Sarah lately but ...
When Bristol said that her mom had made a decision and that she (Bristol) knew what that decision was and that it would stay at the family table until her mom decided otherwise, I got the distinct impression that the decision was not a yes or no decision. I think Sarah decided not to make a decision until she sees one of two things: 1) a candidate enters the race who she believes has what it takes or 2) no candidates enter the race who have what she believes it takes.
She’s said multiple times that she’d offer herself up in the name of service if she felt it was necessary. My guess is that all this waiting is Sarah assessing the current field of candidates and considering the impact upon her family if she has to run.
I think that’s a good assessment. Palin does nothing brashly or impulsively. She has mentioned “people on my team” which leads me to believe that she has people in place should she decide to run.