There is a great Sunset book on this which I bought many years ago. May still be in print. I haven't done drapes in ages so I cant be specific on method.
I am more concerned about use of fleece - what it will look like from the outside of the house and how it will permit light, and how it will hang with cotton for the face fabric. Usually a drape has a lining and possibly interlining which are gauged to the weight of the face fabric. If this is because she wants to keep warm, maybe you could suggest one of the linings which has a vapor barrier. They are lightweight neutral white/cream, would work with cotton, and would hang well and not bunch at the top or sag at the hem, and they aren't stiff. Good luck!