I have been asking myself this question because of her propensity for inflicting pain - you can get the details here.
Truth be told, I have been getting some results lately in trying to get her to stop the madness. I was at my wits end. I applied time outs faithfully, but it didn't seem to be doing much for averting the behavior. I had a talk with my very wise mom, and she advised me not to react emotionally to Violet's violence.
She told me, in her infinite wisdom, to be extremely calm. I had been reacting emotionally and getting angry. Not because I was angry, but because I thought it would make more of an impact if she saw my disapproval very clearly. Apparently not the way to go.
So I started applying time outs as recommended: very even-toned, matter-of-fact, and other words that have dashes in them. And LO! it has been working brilliantly. This, however, is not how I found out the truth about whether Violet is a sociopath. Even sociopaths can change their behavior if they want to, and if it serves their cunning purposes. For all I knew, she was trying to lull me into a false sense of complacency before attacking for real and stringing up the family on a clothes line. I mean, so far, I had never seen her yawn when someone else yawned (a sign of empathy).
But I discovered the truth by one simple method: Dumbo. Say what now? Oh yes, I said DUMBO. Specifically, the scene where the mom is jailed and she tries to stick her trunk out to touch Dumbo. The thing is, the scene is so powerful that I cry every time - because it is just that sad, and Dumbo is illustrated so brilliantly that he really seems like a little child. In case you don't know what I mean, here it is. Get your hanky ready.
So Violet watched this scene, and then came running over to me, tears glistening in her eyes.
"Mom, why Dumbo? Why Mommy? Why jail?" She had actual little tears forming and they were slowly trickling from her eyes. She was...sad. She pantomimed the mom cradling Dumbo on her trunk. "Mommy need her baby!" This wasn't like her usual crying, like when she is upset that she didn't get her way, or like she needs a nap. It was just this trickle of tears leaking from her eyes. And she looked so, so sad. She was...empathizing!
Bingo! And that, my friends, was the moment I knew definitively that Violet was not a sociopath. At this point I am breathing a big sigh of relief. Between the knowledge that she is normal, and my new time out technique, things are seriously turning up roses.