Who is Jillian Mastrano from Bloodlines and what is their importance?

Jillian Mastrano is Vasilia Dargomir's illegitimate sister. She is fifteen-years-old, and Sydney's assignment includes protecting her. Jill and Sydney are sisters and roommates while attending school in Palm Springs. Damien is their brother at school, and Keith is their local guardian and older brother living off campus. Jill reminds Sydney of Zoe, her sister. The girls are similar in age, and Sydney feels the same protectiveness for Jill that she feels for her sister.

Jill and Adrian share a spirit bond, which allows Jill to see what Adrian is doing and thinking wherever he is. The bond they share literally allows Jill to feel the way Adrian feels from what he does. When Adrian gets drunk, Jill has the hangover. When he is sad or depressed, Jill is sad and depressed. In the end, however, their bond is what saves Sydney and Adrian's lives from the Strigoi and Clarence's son.