I went to visit a lady yesterday who was selling her stash. All four walls had shelves, floor to ceiling. You could tell it use to be organized just from finding small "islands" of folded, like color fabric. Some of it had paper pinned to it with the length. She said she used to be very organized and really didn't know how it got out of control. She seemed happy that one of the ladies with me was folding stuff and putting it with "like" fabrics as we moved stuff to look for other stuff. The three of us bought over 400 yards from her. Most of it is for our church sewing ministry, but I did find quite a bit that I bought for myself.
i would ask Grandma if she has any favorite fabrics and where she wants them. She will know where her favorites are even in the chaos, and talking to her about the things she has made as she shows you and start working will probably have her in there helping you if she is able. How do I know this worked, I have a very helpful grand daughter.
it turned an overwhelming job into a wonderful memory.