Just politely tell her its over and done with. there is no use of you two being on the same roof if you are already done with the relationship.
let her know that you would like that to happen but its just not possible since its ex and stuff. Thats the polite way of saying it out and yet still retain the composure for not being rude and obnoxious.
My take on that is that part of you still wants her living with you but its time to jumpstart you life with a big change.