Given your grandmother's year of birth, 1946, it's possible that she was the daughter of an Italian prisoner-of-war. Numbers of such prisoners were kept at Wynols Hill, a few miles from Lydney, in POW Camp No. 61.

At www.sungreen.co.uk/Broadwell/Wynols-Hill.htm there is a photograph of some of the prisoners, and of the associated Marconi Memorial that hasn't survived.

The narrative at www.radiomarconi.com/marconi/aaa4.html suggests that the prisoners would have been brought by train through Lydney, that they were reasonably popular with local people, and that quite a few settled locally after the war.

At www.nationalarchives.gov.uk/catalogue/rdleaflet.asp?sLeafletID=78&j=1#7, paragraph 7.1, it says that alphabetical and numerical indexes of Italian Prisoners of War were sent to the Italian Red Cross. It goes on to say that those records were then dispersed, but it also gives an address where you might pursue your enquiry.

There were Italian Families living in Lydney and Coleford late 1940's 1950's & 1960's.