As of tomorrow night, Cassie will not quite be herself.
In fact? She's going to spend the next few days been a manipulative bitch. Fun, huh?
She's gettting herself all possessed. As will happen when you have someone like Azazeal following you.
So, after Wednesday night, she'll be hitting on people all over the place, manipulating those she thinks she can, and generally being a horrible person. This is the first way you could get your characters involved.
The second way, is as part of the depossession attempts. Canonically, there are a few unsuccessful electrocutions, orchestrated by Thelma over a few weeks. We're sort of... condensing all this into a few days.
The actual final depossessing has already been planned and set for Monday, but if you want to help out with a subtle and unsuccessful attempts over the few days beforehand, at getting whatever evil has taken over the girl out, I'd love to get some others in on all this.