On imdb they report Liz plays Erica Evans.
VISITORSITE updated the cast’s page with this info:
Elizabeth Mitchell as Erica Evans
Even though some news sources are claiming that Elizabeth Mitchell will only be a guest star, the role of homeland security agent Erica Evans is a huge role for the series and could mean the end of her run on LOST as Juliet.
Erica Evans will not only face a new mystery with the Visitors – her son, Tyler, might become involved with them, much like Daniel Bernstein did in the original series. Stay tuned…
I don’t know what that’s supposed to mean for Juliet’s fate! What do you think?