A couple of other things I noticed are (and oh, had I KNOWN before! But better late than never, and I hope they will help someone avoid the danger):

-Exaggerated expressions. If they sound too good to be true and are inconsistent with her actions.

-"The look." Like having a grin on her face at an inappropriate time. She looks at you as if you are being ridiculous or as if she is enjoying seeing you aggravated.

And if she acts "concerned", but it doesn't feel sincere, try looking away for a while or excuse yourself briefly. She will either have an expression of hatred on her face, or a grin from a sadistic pleasure, as soon as she thinks you are not looking (Hmmm, what happened to that look of concern she just had?)