Don’t mistake this for empowerment. I believe this is Janice’s psychotic personality changing gears. She sodomized Ralphie because that’s how she could control him. She showed the same control-by-sex skills with Richie, who liked to hold a gun to her head during sex. She controls these kinds of men by giving them what they want in bed so that she has something to hold over their heads later, even if only implicitly (“You’ll do what I want because I’m the only one who’ll do what you want”). Once she started longing for Bacala, Ralphie became an impediment to her and had to be gotten out of the way.