Haven't seen the movie so I don't know but I have read a Christian book that said that Lucifer has already been bound up by the archangel Michael so it is not possible to be truly possesed by Satan or Lucifer. They are being held on a prison planet and will eventually be wiped out of existence unless they show some remorse for leading the rebellion on this planet which they say is unlikely. I know most Vaisnavas I have talked to say their authorities view Satan as a Christian myth. Maybe she was being bothered by some demonic entity and some how she associated that entity with Lucifer or something who knows.
I have personally seen 3 hovering black entities when I was in a mental hospital. I think part of that may have been hallucinations due to the anti-psychotic drugs I was on so I don't if what I saw was real. Don't know for sure if I was possesed or what but I had all sorts of evil thoughts but looking back on it I realize my major problem was that I had too much attachment for my girlfriend who ended up cheating on me and that caused me all sorts of anger and other negative feelings that either let in an entity from some other plane or just brought out the negative aspect of my own nature. Ultimately it was my own fault for getting involved with a slutty woman. Lesson learned, Prabhupada was definelty right when he said women can be the doorway to hell.