Thanks, Sminky.
The info is beginning to build.
I've always been convinced that HC wrote 'My Rattling Old Black Mare' as a parody on 'My Old Wife and I' after falling out with one of his wives. About the same time he wrote 'My Mother-in-Law'. It might now be possible to put much more meat on these bones. Off the top of my head, if this is the case, Mary Ann Terry looks to have been the victim.