Friend of not, if she

“Lucky you,” she said. “I never get away. Well, hardly ever. Dieter’s taken me for a pint of half-and-half at the Thirteen Drakes a couple of times, but then there was a most god-awful flap about it. The POW’s are not allowed to do that, you know. At least they weren’t during the war.”
“Dieter told me your sister Ophelia had him to tea yesterday,” she added, somewhat cagily. I realized at once that she was fishing.
“Yes,” I said, kicking carelessly at a clod of dirt, gazing off into the distance, and pretending I wasn’t remotely interested. Friend of not, if she wanted gossip from me, it would have to be tit for tat.

***
What’s the meaning of the highlighted?