Dr. Jane Whitcomb (a.k.a. "Doc Jane") is first introduced in "Lover Unbound" (Book 5 of the series).
Jane is the eldest daughter of Drs. Whitcomb. She had a younger sister, named Hannah, who died when Hannah was a child. No other living blood-relatives have been revealed to be related to Jane in the series to date.
Jane is a highly skilled trauma surgeon and the private physician of the Black Dagger Brotherhood. She is a human female, who through a series of unfortunate events, becomes a ghost with a corporeal form by the end of "Lover Unbound".
She is mated to the Black Dagger Brotherhood warrior, Vishous.
As a child, Jane asked a Ouija board who she would marry and it spelled out "V-I-S-H-O-U-S". How that happened is never revealed in the story (speculation is rampant throughout the fandom that it may have been an unrevealed guardian-type angel -similar to Lassiter or those from J.R. Ward's "Fallen Angel series- or the Scribe Virgin, herself).
Jane was devastated by her younger sister's death. Hannah's illness is what inspired Jane to go into medicine, in fact, although she deviated into trauma surgery, rather than oncology.
As an adult, Jane obviously passed the New York Medical Board's requirements to become a trauma surgeon. At the beginning of "Lover Unbound", she is working at St. Francis Hospital (where she served her residency and worked before that is unspecified in the text). At St. Francis, she is supervised by Dr. Manuel "Manny" Manello, who is Chief of Surgery for the hospital.
It is clear almost immediately in "Lover Unbound" that Dr. Manello has feelings for Jane that extend beyond platonic employer-employee bounds, but that those feelings are not returned (although Jane does have an incredible respect for Manny as both a person and a doctor, and they are extremely good friends).
"Lover Unbound" introduces Jane as the trauma surgeon who is brought in to handle Vishous' case. He is brought into the hospital after an alteracation with a Lesser goes wrong and Vishous ends up getting shot in the chest and nearly killed. As she examines the X-Rays, she begins to notice how different Vishous is from a normal human male. She operates anyway, saving Vishous' life.