Dev is a very volatile and generally hard to pin down person because she suffers from Borderline Personality Disorder and Bipolar. Which generally mean her moods fluctuate daily,even hourly, and very extremely.
She is a naturally very hot-blooded person, regardless of what state she is in, and vulgar to say the least. Shes very simple in that sense. Dev is a thrill-seeker and loves everything gritty and wild. Pretty reckless, too and with little sense of self-preservation, or rather considering how suicidal she is, probably none at all. Tries to inspire the same kind of reckless abandon in others as well.
Still, she enjoys a lot of traditionally feminine things as well, which might contradict her overall persona.
Though you would think her an extrovert, people can and do tire her. Though to most she would appear as a pretty stupid and simple individual, a lot of deep thoughts zap through her brain, though largely very morbid and sort of disconnected with reality. Shes surprisingly philosophical and enjoys writing poetry or jotting down her own thoughts when she is alone,  asks other people strange, deep and intrusive questions sometimes out of genuine curiousity. Very thoughtful, just not when action or emotion are concerned. Has little in the way of regret or understanding of consequences.

 The creature that has taken root in Deneuve's mind, been there since she was a child. She calls herself a vessel of it, and the manifestations of its powers " L'appel du vide". The Call of The Void. It's call. People around her just cant seem to help their own compulsions. All the intrusive thoughts, impulses get magnified, and their actions are the offerings to feed the supposed god. Inexplicable things after all seem to happen around her constantly. Be it people picking up gum off the pavement or someone swerving their car into an opposite  lane.  

Those involved with magical thinking, otherworldly concepts, occultists and those of supernatural origin themself, who are used to seeing the world in a different way seem to feel this influence less, if not at all, depending on the individual. It is born of the mind, after all.