Ethan was most definitely a fool, there's no argument there. And though you do make a rather good point about them being more of a nuisance than help in this instance, I still think that she should have expected that to happen - them storming to help her and falling in a trap.
Madame Kali: "They'll be here soon".
Vanessa: "Who?"

Self-obsessed much? Who do you think, you idiot? Friends you forced to come.
In truth, I don't know... I am still very pissed that Sembene is dead, so I might be too harsh on her right now. It seemed she felt it was her fault that Malcolm did his idiotic storming on a mansion, so her judgement was clouded when she, ironically, did the same.
Oh and, as for her not knowing in what manner is Ethan different, she have seen what Ethan did to Roper in this episode. And two episodes ago Ethan had to storm out of the house, because he was noticeably barely able to control himself.