Maybe woofgang has a point there.
Is she a bit obsessive when it comes to switching things off? I can't have anything with a light on, when I go to bed. Nothing to do with cost, but more of a very annoying OCD issue!!
I have to pull the (very heavy!) chest of drawers out a bit, just so I can get to the extension lead plug that's plugged in behind it. It's got a light and I'd never be able to sleep if I thought it was on.
So yeah, she could be doing it for cost... or she could be as weird as me :P