From the Official www.TomCruise.com:
Entertainment Weekly reports that the actress (who’s on Variety’s list of 10 Actors to Watch) will return to the show to play Shannon Rutherford, a role that helped launch her acting career. The show’s producers will not say how many episodes she’ll appear in, but fans will surely be delighted to see Grace again after her character was killed off in season two.
It’s even more knowing that the Lost on TV as we know it may not have turned out that way if it weren’t for Tom! J.J. Abrams, the creator of Lost, had to drop working on the project full-time in order to direct Mission: Impossible III with Tom. As a result, executive producers Damon Lindelof and Carlton Cuse took over as show runners.