if you want to claim rent-a-room for your OH living in your place, then you'll have to sleep in separate rooms to be eligible! If you are both sharing a bed(room), then obviously she isnt renting a room of her own to sleep in.
Beware of all those Revenue/SW catch all rules which, in line with the Constitution, mean co-habiting couples cannot be in a more favourable position than married. Married cohabiting couples cant claim rent-a-room for each other, so it follows that non-married cohabiting couples definately cant.