Personally, I have never understoood the idea of giving up my bed for guests. My bed is MY bed and my room is MY room. Guest get the kids beds, the couch or even an air matress, but NOT my bed. I have had others give up their bed for me when I was a guest and it made me extremely uncomfortable.
There maybe a point where you need to stop treating her as a "guest". Someone once asked me specifically to strip the bed I was sleeping in before leaving and now it's just automatic. Don't be afraid to ask for what you need in your home and that goes double for relationships(no matter how awkward).