Hi
I have looked up your relative. I am assuming that this is the same lady:
Born 21-Jul-1881, Studley, Warwickshire
There is a note on the record (Home Office: Aliens Department: Internees Index, 1939-1947 - HO 396/81) which indicates that she was interned because she was on holiday in England in late August 1939, and that her son, although born in England, was serving with the German Air Force.
It is dated 15th August 1940. She was living in New Eltham, SE9.
From another document (HO 396/275) it appears that we was moved from Holloway prison on the 9th September 1940 to the Isle of Man. She was then authorised for release on the 30-Jun-1941 and recategorised as 'B', and released on the 8-Jul-1941.
I hope that helps
Matt