I think Palin is waiting for her good friend Michele Bachmann to drop out first.
Some friend. After Palin campaigned for Bachmann in her 2010 congressional re-election bid, Bachmann went on to declare for president, then said nothing after her rabid campaign chairman slandered Sarah on radio.
For what it's worth, I don't think Sarah lost much sleep over it, and probably even forgave Michelle in her heart.
I highly doubt that Sarah is waiting for Michelle to drop out of the race before she enters. If that were the case, pressure would be put on Michelle to stick it out until the early filing deadlines had passed, to keep Palin out. But - that's probably just as wild a theory as the one you just proposed (no offense).