I pretty much could use my entry from two years ago for this, since I think I also used the Joubert family then.
Sylvia's mother moves her young family to the south of France (outside of Marseilles) around the year 1500, when Sylvia is three years old. She has two older sisters: Agnes and Sophie. For the first couple hundred years Agnes is kind of a scatterbrained bimbo, who has a number of affairs with "mortal" (ie nonmagical) men over the years. That is until she finally finds the love of her life and settles down. Sophie is a know-it-all bookworm who comes to a bad end in a town called Salem, MA--or does she?
Sylvia walks a rougher path than her sisters. Her skills are uniquely suited to "offensive magic," so she becomes a hunter of demons, bogeymen, vampires, and so forth. Interspersed with this she has a couple of love affairs that both end tragically. She travels all over the world from France, through Europe, into Egypt, and later even to the Old West. But all the time she spends alone helps her to see the value of her sisters.
A lot of the material for this book came from the first draft of the 5th Scarlet Knight book, later to be known as Betrayal Begets Blood. The flashbacks to Sylvia's old life were really too long, but I always thought they could make a good novel on their own. So eventually when I got done with the first drafts of the Scarlet Knight series I wrote that book. It has some of the weaknesses you'll find in any prequel, but I think it's still a good standalone book.
The second tragic love affair for Sylvia I pulled largely from Possession by A.S. Byatt, which I bought from a library sale for like $1. There was a movie from about 2002 with Gwyneth Paltrow and Aaron Eckhart, which I bought on VHS a while back because I don't think I could get it from Blockbuster or Netflix at the time and the DVD was expensive, though now it's only $10 on Amazon or you can rent it for $3. Anyway, both the book and movie are pretty decent.
Because I felt lazy I pulled a couple excerpts from this book to put into the revised Betrayal Begets Blood, which looks kind of weird because Sisterhood was the first book I ever wrote in first-person present-tense while the Scarlet Knight ones rely on old-fashioned third-person, past tense. I didn't feel like going through to change all the tenses and stuff because what the hell they're flashbacks to Sylvia's life, so why not let her narrate it in first-person?
This and the rest of my books are available at the new Planet 99 Publishing site!