Hi Glyn,
it is not a German custom. I know that we can do this here in Germany, but I don't know anyone you did it or hear about it. Are you sure she had dug up her husband and reburied? On German cementries you often find gravestones with names of their family members who died as a soldier in WW2 somewhere else. The families do this in memory. But there are only the names (with birth and dead) on the gravestone.
These days we reburry people from WW2 which were found in the forrest or somewhere else. But this soldiers hadn't have a regular grave, they were not buried on a cemetery. In Germany still 1 million soldiers from the WW2 are missing today. For more information about this please look here
www.volksbund.de On the right side above are flags, there you can change the language.
I hope you understand this, it is not so easy for me to explain it in English.
Betty