She probably loaned money to Simon's siblings for tax purposes/Centrelink purposes.
I can’t get into the loans as I don’t know the details - it is still more a “he said, she said” situation and invites more questions than provides answers. However, I remember a totally different episode. Does anyone have any recollection of the time when Erin used to edit a local news leaflet? She complained about the locals to her online female friends. Poorly educated, and why was she even doing it for them… This is where I thought, you either do it or you don’t, but why do it and then, get irritated with the people who are reading it?
JMO, Erin is smart but she also has to feel that she is the smartest one in the room. Remembering what Simon said about Erin having poor self-esteem, being the “smartie” could have been her way to compensate. Allegedly between her and Simon, she was the organizing power, but Simon was a civil engineer, so, quite a match for her, IMHO. Yet she really self-asserted by putting him down (remember how she lamented, she invited people to clean the house and he didn’t notice, such stuff.)
So coming back to money. I don’t know what was the purpose of her loans to his family, tax is the first thing that comes to mind, but maybe, she was not minding the loans at first because it was in 2007, and at that time she viewed the Pattersons as her family. Financial relationships are so hard to understand, we probably shouldn’t even try, but I strongly suspect that at a certain point, she felt taken advantage of. And this where her cluster B-type anger must have become overpowering. She had an accounting degree, she was doing the taxes, she was independent and the money was hers. This is when she probably saw red.
Did she expect to improve her financial situation by killing them all, or was it a mere splitting where she and her kids were on one side, and the rest of the world, on the other one, hard to say. Perhaps just being angry with the Pattersons for all, perceived or real, financial transgressions, could have been enough to decide to kill them.
So ultimately, I think that these were her poisonous Cluster B traits that were the reason behind her crimes.
Who do you see as her parallel? Maybe Kaitlin Armstrong?