While details of her resurrection are scarce, it would appear that her appearance would likely appear in flashback or possibly hallucination form. It is believed that she will appear in the season's second episode, where Cheech Marin is also scheduled to guest star.
Rodriguez isn't the first Lost actress to come back from the dead. Last season, Cynthia Watros' Libby character appeared in a vision of Michael's (Harold Perrineau).
We'll be sure to keep you posted as more details surrounding this interesting resurrection arise. The fifth season of Lost is set to premiere at the end of January 2009.