Who is Elizabeth Osbourne from The Mark of the Assassin: A Novel and what is their importance?

Daughter of a liberal U.S. Senator and prominent Washington D.C. attorney, Elizabeth is married to Michael Osbourne. She is not thrilled with his occupation but tolerates it because he is, at least, assigned to a desk job at CIA headquarters. More than anything, Elizabeth wishes to begin a family and is undergoing in vitro fertilization toward that end. The procedure is not attended Michael, as he is off in Europe chasing his old nemesis, who killed his first love, Sarah. Elizabeth is certainly concerned that Michael has never recovered from Sarah's death but remains steadfast in her love for him.