Two Words - Brokered Convention.
Palin is letting the nominees self-destruct, throwing enough hints about supporting Gingrich to keep Romney from locking in the nomination. The HBO hit piece movie (Game Change) was probably timed to sink her nomination; with her not running it will draw a yawn from the media and be old news by the convention. Then she will step forward and be the only candidate not damaged by the nomination fight.
About time for the media attack machine to start on Santorum - if we are lucky they will try to make hay of his daughter's health as a reason he can't concentrate on the Presidency. That might backfire ....
A brokered convention is undoubtedly what she is pushing. Her conditional support for Gingrich, “to keep the process going” was a clear move to get to the convention with no clear winner, and everyone looking for a acceptable compromise... i.e.: Sarah P. Works for me.