How to get rid of my housemate? ?

Buy her a space heater for her room, that way you aren't running the furnace all the time. if that doesn't work be nasty and turn the breakers off for the washing machine.and put a lockable clear plastic cover over the thermostat with a key lock. that she won't have a key for. She may get mad but hold your ground, you out number her. It really is a problem when you have a self centered person, that won't compromise, as you found out.