The Dead Cast No Shadow by Marlene Pardo Pellicer

Her name is Ema, The Walker Between the Worlds. In the Supernatural Underworld she is known as The Lady in Red, or if you were a vampire being hunted by her The Lady of Blood.
For hundreds of years she's fought every hellish creature that's crawled out of the The Pit, especially those that hide among humans using them as avatars.
Her allies are few, like the sometimes treacherous members of the Sempiterno Apostasy.
Still in mourning over the death of her last sentient avatar Mort, she is approached by one who is running from a childhood encounter with the darkest Evil as he tries to unravel the mystery of his brother's murder.
When the danger to your body and soul hangs in the balance, who better than a fierce warrior who is the bane of Hell to be your bodyguard?