My article dealing with this subject has already been linked to, and I encourage those interested to read it; but here is the pertinant quote:
One of the first references to be found on women wearing the sash is from The Kilt: A Manual of Scottish National Dress, written by Loudon M. Douglas in 1914. He writes, “It is desirable that ladies who wish to encourage the Scottish National Dress should wear sashes of tartan, with evening dress. These should be preferably worn over the left shoulder and fixed by a circular brooch. Other applications of the tartan in connection with ladies’ costume must be left very largely to personal taste.”


And I think it should be left at that. When women ask me whether someone might criticize them for wearing their sash the wrong way, I always ask what boar would dare tell a lady how she ought to dress!