Ben, (like his predecessors) sends agents off the Island as required. Greta and Bonnie("Greatest Hits") were allegedly on assignment in Canada. Mikhail thought of dispatching agents as routine and was surprised to learn that they were still on the Island. Jill is such an agent, on assignment at the time that the Island moved.
Jill is one of many Others who were off island when it moved, and are still allied to Ben.
Jill is Annie, evidenced by her face and attitude and the fact she appears a similar age to Ben.
In the casting call Jill is described as "Late 20s to late 30s; ANY ethnicity." If she in fact was Annie they'd be looking for a Caucasian lady.
Is one of the many others who are off the island, and apart of a group who got information on Widmore, and the Losties files.
Jill is actually a Widmore agent and has informed Widmore about Ben depositing Locke's body and major aspects of Ben's plan to get the losties back to the island. We will see that Widmore agents were on flight 316 as a direct result of Jill's intelligence.