That sounds like Unity Mitford whose father was a Baron.
She was a friend of Hitler and was a member of his inner circle of Nazis, BUT her and Eva did not hit it off together, which seems to tie in with your story.
For some reason she tried to commit suicide by shooting herself in the head with a small pistol given to her by Hitler, but somehow (!) survived and was flown back to England where she lived until her death just after the war.
EDIT
And before anyone mutters Wiki, my wife was fascinated by the famous/infamous five Mitford sisters and over the years I had to buy her every book I could lay my hands on about them. There's also been two or three documentaries about them too. Broad spectrum of politics between them, from extreme right to extreme left and probably the most well-known, because she lived until a few years ago at Chatsworth House was Deborah Cavendish, Duchess of Devonshire.