Good theory, but how can that explain how she wrote about her death?

I see it more like Albert as a human, the snake a metaphor for how evil he is, just a thought though.

I can see this as trauma, Albert molesting her and her aforementioned death could be her losing her innocence and past self.

Father and Mother = Albert somehow? Like a cult or something? And the journal is them trying to fuck with the cops? Or Multiple personality disorder?

Something occult perhaps? Like metaphorical to, eg. Adam and eve, the serpent, the forbidden fruit, the biscuit, I can't figure it out, but it's some sort of heavy metaphor.

One thing that confuses me, Albert couldn't have wrote it, because the dad killed him, is it possible, maybe, edie was stalked and molested by another dude as well?

I believe you're right, heavy metaphors here, I think Albert is a "snake" who is a "Predator" aka Pedo, the venom can be a metaphor for bodily juices, incredibly disturbing..