According to most websites, this is all but a done deal.
I kind of have mixed feelings about this. Although I'm sure she'll do well staying in IRL, I can't help but feel that this will be a dead-end for her. IRL is in some major financial trouble. Top that off with the stands being mostly empty at every race except for the Indy 500. The IRL really needs a lot of help to stay afloat. At this rate, they've got maybe 2-3 more years left.
I think NASCAR was a long-shot for her. Although she could have made a lot more money, I don't think she's the kind of driver to adapt-well to the heavier stock cars. She would have been winless for a long time, if she won at all.
But I'm more than a little surprised that she didn't go with the USF1 team. A new team just starting out needs star-power, and that's something she could have provided. Besides, with the lack of pairity in F1, she could have finished outside the points every race, and it would look perfectly normal for a driver not in a Ferrari.