A step mother who tends to control people who they have no right to control, such as step children. The step bitch is known to control the biological father of said children to a point of totalitarianism within the household.
"Tom told me that the lady his dad just married is turning out to be a HUGE controlling step bitch!"
"I can't believe Carrie, what a step bitch, jeopardizing my relationship with her step daughter!"
"My step bitch is making me do all the chores because she thinks I don't do anything!"