A very dark piece you have here. The writing could do with some tightening up, its a bit long winded at times. The dialogue too was a bit ripe, the characters a little sketchy, as if taken straight from Hicktown Central Casting. The titular Bonnie had some depth to her though and consistently surprised me in her actions and words.
As for the story itself, it came off like a twisted, deep south version of A Christmas Carol...but without the hope or moral lesson. I'm not saying you must have that here or it would necessarily improve but as it stands, things start bad and progressively get worse for the characters until they're summoning satan to smite their enemies. Again, I don't need redemption but this is without reprieve or push back, a linearly descending trajectory. As a result it becomes a bit gruelling and, in the end, sort of pointless.
There is nothing much to wrestle with here, nothing to really chew on or consider. Basically, these are people born into unfortunate circumstances which perverts their innocence, turns them into monsters who then inflict violent revenge of those who made them like that, a self destructing cycle. One can only imagine how Bonnie's daughter is going to turn out.
The Carrie like ending and whether it happened or not seems superfluous and doesn't really have any bearing on the story. Other then it being a chance to do some cool visuals an deliver some grandiose dialogue it serves no purpose as far as I can see.
I do admire how far you go in the flashback scenes, how depraved and dehumanised Bonnie, and her world, gets, I just wish there was some opposing force, something or someone to balance the story, give it dimension.