That would be a horrible piece of data to base a "run/don't run" decision on, as Bachmann has absolutely zero chance of winning the nomination, even in this weak field. I think Cain has no chance either, but he'll be a real contender long before Bachmann is.
In my opinion, the only "stumbling block" for Palin would have been Huckabee, not because they are similar, but because a significant portion of their respective bases overlap. With Huckabee out, that dramatically increases the odds of Palin being in, if indeed she is basing any part of her decision on the moves of the other potential candidates.
I am just speculating that she may figure the two have so much in common, so why run against her? That she thinks that Bachmann cant win the nomination and that will shape her decision is similar speculation as mine.