A partial index of discussion notes is in http://www.cs.bham.ac.uk/research/projects/cogaff/misc/AREADME.html
Originally she used OpenOffice, but when that was taken over by Oracle, and before it was handed to Apache I switched her into using Libre Office instead, on the advice of colleagues. That worked well, except that at some stage, I am not sure exactly which stage, she lost the ability to launch LibreOffice automatically by clicking on a file of a type that it can handle. Instead she either had to launch LO, then use the 'Open' dialogue, or else use 'My Computer' to locate the file and 'drag' it onto the LO desktop icon.
When I tried to set up the file associations in the normal way it would not show me LibreOffice, and even if I used the browser to select the LibreOffice soffice.exe executable, it did not work.
An internet search soon revealed that many people had the same problem and a common thread was changing from OpenOffice to LibreOffice followed by the file associations not working. There were many fixes offered on various web sites, including reinstalling LibreOffice, running it's 'msi' program, making sure OpenOffice had been removed, and possibly others, none of which worked.
Fortunately a recommended free registry cleaner is available from CNet and since I could not find any warnings against using it, and I believe CNet is reputable, I fetched it from here.
When I ran it I unticked all the offers of information, and then after clicking on 'Next' (or whatever the button was) I found it offered me some other software, with a 'Next' button and a 'Decline' button. I clicked on 'Decline' expecting the whole process to abort, but it didn't: it continued downloading the required installer, which installed the Fixer without any problems. I ran it and selected the complete scan option. It seemed to find hundreds of rubbish files in the registry, and selected them all by default. So I trusted it and continued, finishing very quickly.
After that I was able to go through the usual procedure for setting up file associations, either using 'Open With' and selecting the 'always use' button or, or else following the procedure recommended by 'Digital Dave's' answer here
I hope this information is useful to others and that they will find this in less time than it took me to find the solution. The next option may be even better.
School of Computer Science
The University of Birmingham