I am just brain storming here - what if you make it like an envelope pillow style? Thinking that she is going to make it like a duvet cover, so the batting can be removed like you would a pillow. It would take a lot more fabric for the back but you wouldn't have to deal with fasteners or zippers.
We were in Berlin this summer, we stayed in a few places and each one we had what looked like a king size bed, but they were 2 twin beds in a king size frame and the quilts were 2 twin quilts that went together, so we each had our own. (I know I am not explaining it very well.) I really liked it and will consider doing the same thing here. My husband has wanted a king size bed for years but I cannot deal with the weight of the blankets.