Mark,
Dont mean to be negative, but I doubt anything will remove the stain, because thats what it is, and I think you have already tried most things. I wouls have thought that if the first two attemps didnt work, then nothing was going to remove it completely. You warned her beforehand that you may only be able to improve it, but she now says its worse. Of course this is rubbish, it may just be more noticeable (even though you have reduced it) because you have removed the general soil layer that was helping to camoflage it. As is common with lots of permanent marks and wear areas, they can become highlighted following cleaning.
Dave.