All the traits you attribute to sociopaths can be attributed to psychopaths and vice versa. Moreover, coldness and calculating are not necessary traits of psychopaths, they are cliche from the popular media.
Now, I'm not a psychiatrist, so you can take anything I say with skepticism. But as far as I know, there is no established distinction between psychopath and sociopath. Both are synonymous with antisocial personality disorder, yes. But what is now called APD used to be explicitly called psychopathy. Sociopath is not a formal term. Sorry if you think I'm trying to act smart-ass here, but both words have been used differently so many times that their meanings is completely blurred now.
From an average point of view, I think it would be accurate to say that the stereoptypical serial killer is a psychopath, but the person who calmly steps over a dying body to get to his car is a sociopath.
There's no way Bella has APD. Given her feelings, which she shows to Nika and her sister, this is simply impossible. If you want to see how a person with APD really interacts with people, I highly recommend you to watch Nightcrawler. This is the most realistic depiction of a sociopath/psychopath who is not a typical serial killer. It's also a great movie. Or just watch these scenes
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. Judging by them, Vanessa could be in this guy's place. I didn't think so at first, but after you mentioned it, I can see Vanessa has APD, easily. But it's too early to judge for sure.
The situation requires is the key here. She changed her behavior because she suspected Bella is one thing, she changed her behavior because she views Bella as upper/lower class is different thing.
Here I was writing an epic reply. "What the hell are you talking about?" "We were arguing about whether Vanessa was intentionally hostile to Nika" blah blah blah. Then I opened the dialog file.
Bruh.
So yes, you were right and I was right, she was intentionally hostile to him, but because of the way he looked at her.
The longer we wait for the final version, the more we forget and the more pointless debates we have.
But hey, now you can lower your Vanessa is evil rating at least 80%. 85% considering you were half right.
Yeah he sure does.
However, I noticed something when I was reading the dialogs. Bella mentioned that Stefan lusts after her mother. When I remembered how weird Amber was acting with Nika, and I was like

. I mean, during my playthrough her behavior didn't seem odd to mee because this is an adult VN. But maybe in the context of Bella's hatred towards Stefan, the problem is actually Amber?