I think she's going to turn out to be Daniel's mother, who Desmond was told to find at Oxford. She seemed to be doing physics related things in the basement of that darkly lit church place.
I'm not sure how I feel about this whole "island moving in time" deal...the plot arcs are getting a little too sci-fi for my taste, but this still promises to be an awesome season...it's a character-driven show, and all the actors seem to be in top form.