Yes.
So, it's hard to know what is and isn't true in the things that Isabella has said. This is because, in addition to being a psychopath, she is also a pathological liar. But, I'm going to assume that the things she's said about her relationship with her father, as opposed to who her father is, are things that have been true.
Their relationship is wildly inappropriate for a parent and child. She has said that her father uses drugs in front of her, possibly with her. She has said that her father has watched porn with her - I believe how she phrased it was showing porn to her, with makes it of his own volition and very intentional (and I don't think she's smart enough to even think about something like that.) She has said that her father has told her about his sexual conquests. (And we know for a fact that her father has told her about seemingly every war crime he was involved with.)
On their own, these would be deeply fucked up. It's in conjunction with everything else that they're horrifying.
She displays hypersexualization. She has a paraphilia for incest, but she seemed to be legitimately disgusted and outraged once incest was actually taking place. She has several paraphilias involving waste, and very intentionally neglects her hygiene to a level that's unheard of outside the severely mentally ill. She doesn't shower, she soils herself and doesn't clean, etc, etc. She alleges to have engaged in coprophagy. I strongly suspect that she self-harms, based on photos I've seen, but can't recall if this was confirmed. She abuses animal, and is manipulative and violent towards other people.
Minus the shit-eating, I have known plenty of girls like that. You don't just wake up like that one day. Without exception, every one of those girls was abused, sexually, by a parent. I know that everyone likes to believe some people are just Bad Seeds, and while they do happen, what you usually learn about 'Bad Seeds' is that all the awful shit just happened behind closed doors in a family with a great reputation and even better damage control.
It's a kind of abuse that's more common than anyone is willing to admit. Generally - to be blunt and callous about it - generally, 'you' end up one of a few different ways: asexual because you reject that aspect of yourself altogether, reflexively gay based more on hate for sex X than attraction to sex Y, hypersexualized because you perceive it as control of your sexuality (or, more depressingly, 'the only thing you're good for',) addicted to drugs, dealing with the trauma in a "healthy" way, suppressing the trauma entirely (and dealing with a whole host of other psychological problems that arise from that), dead, or the unfortunate standby, becoming an offender yourself.
But to end up with all the things present in Isabella, you don't just need abuse. You need extreme, open, continuous abuse. The girls I have known who displayed those sort of signs, are the worst abused people I've ever known. I mean some absolutely soul-killing, should've-buried-them-under-the-jail sorts of shit.
So, yes. Yes, I think he fucked his daughter. And I think that was just the start of it.
(I also think I might know why he could be behind the DDoS, but it reads as tin foil even to me.)