The 1939 Register was used by the NHS from 1948 until sometime around 2000. Her name would have been changed when she married in 1945 by the NHS. The 1939 Register you see on line is, I think, taken from the info which was on it when the NHS stopped using it. It is not just the info given in 1939, which is why you get the name changes on marriage. Hope that makes sense.
Emeltom