Chris Cillizza points to a major hurdle for her in the first primary:
New Hampshire has an open primary system, meaning that independents can choose to vote in either the Democratic or Republican primary for president. ... With Obama almost certain not to be challenged for his party's nomination in 2012, independents are likely to play a very influential role in determining the Republican nominee. Palin has struggled mightily to court independent voters since the 2008 campaign; a recent Quinnipiac University national poll showed just 33 percent of independents viewed her favorably, while 50 percent saw her in an unfavorable light.
But Romney is next door and gives her an alibi. It's way too early to game this, but I see no real impediments to her taking over the party completely. She already has, in so many ways.