The thought process about which you are asking is actually outlined in Chapter 8 instead of Chapter 7. Patty justifies the fact that she is not a spy in her own mind by reasoning that she is not giving information to the Germans, and that Anton is not exactly a Nazi; he is only "a captured German soldier".
Having committed herself to helping Anton, Patty is uneasy. The day after she sees that the prisoner has escaped and steals some food from home to bring to him, Patty spots an article in the Memphis newspaper with "the biggest, blackest headline (she'd) seen since Pearl Harbor. The article describes the capture of a group of Nazi saboteurs who had planned to wreak havoc at a series of industrial plants and department stores during rush hour "to create panic and to break the morale of the American citizens". The article ends with the warning that "the Nazi invaders will be dealt with swiftly and thoroughly...the Justice Department will try the men for treason...any person acting as a spy in wartime shall suffer death".
Patty is already feeling guilty, and the news article only makes her more fearful. It is then that she tries to justify in her mind that despite what she is doing, she is not really a spy (Chapter 8).