I don't recall hearing about her carving 666 into her head, in the past, but just learned about it on this thread. You're right, it's insane. That's one thing I don't think Rusty did himself.
She listened to "sermons" which stated that women are sinful, they are bad, if they are bad their children will be bad and go to hell. Andrea internalized this message, and her mental state grabbed the ball and ran with it. She believed at the time that she was sending her children to heaven, before she had the chance to turn them into bad people because of her "sins". I have some experience about how bad religious beliefs can become ingrained and harmful.
I am so sorry about your half sister. It brings up what I said yesterday about laws prohibiting involuntary commitment. Extremely dangerous for all concerned, and they need to be changed. Your father must be heartbroken over this, as I'm sure you are as well :(
It's really my dad and half-brother who bear the emotional burden. She's about 15 years older than me and I barely knew her at all. I know she visited us a few times during school breaks, but I was too young to remember it directly. Pisses me off plenty, though, that my dad and brother pay tons of taxes, a lot of which go to medical care and other support for deadbeats and illegal aliens, while their daughter/sister who really needs and is entitled to care can't get it because the idiot leftist courts insist she's freely choosing to live the way she does.
My dad actually managed to get a Texas court to have her hauled in for an involuntary psych exam, which naturally resulted in a diagnosis of schizophrenia. Not only did this not result in any Texas agency taking her off the streets, but the court said it can't share the info with federal agencies due to her "privacy rights", so she's not eligible for any Social Security disability or Medicaid benefits. And naturally there is no federal agency with authority to arrest her and make her undergo an involuntary psych exam. Convenient, huh?