This show has trouble getting to the point, but her father is likely Dmitri. He sort of alluded to it, and the show made a point to say only female vampires were infertile but no mention of males but one can assume. We know Vanessa can't be turned because the likely vampire blood that was not passed onto Dylan. The only thing that could make this family more dysfunctional would be if it turned out Rebecca was Vanessa's mother prior to turning.
shareAs for Rebecca, I would be very surprised if she turns out to be Vanessa's mother back when she was human. If Sam's obsession for Mohamad is any indication of their past bond, Rebecca doesn't seem all that interested in Vanessa, except for her abilities as an hybrid.
As for Dmitri, someone else here suggested the same thing. You could be right. The fact that he recognized Vanessa "at first sight" (I don't remember how Dmitri phrased it), and his immediate mention of Vanessa's mother made me feel that Dmitri has more complex interests in her, compared to Rebecca. Is this what gave you this idea about Dmitri ?
demitri could've recognized vanessa for the purpose that her mother fought him, the line of van helsing. He indeed alluded to a vampire being her father but does it mean him or someone else?
If he was her father, why would he be with a van helsing when he supposedly has been fighting them for centuries? & why would he want to dissect his own daughter?
Let's go get a drink & smoke a cigarette
I suspect Rebecca is her mother as well.
Deep down I think she wants all the vampires dead but is it doing it her own weird twisted way.
I think Dmitri raped her and turned her into what she hated most. I think he broke her the way he intended to break Vanessa.