Shelter Island (Cold Ridge/U.S. Marshals #6.5)
Carla Neggers

Boston doctor Antonia Winter has a feeling that someone is stalking her. Thinking someone sees her as a means of derailing the senatorial hopes of her boyfriend, Hank Callahan, Antonia leaves Boston for the secluded wilderness of Shelter Island.
This story is also available in a paperback 3-story anthology, "On the Edge" (ISBN: 9781551667119) which also has stories by Heather Graham and Sharon Sala.