Curious, I posted this earlier and it disappeared.

Passing through customs at Pearson into the US with my wife once, an elderly woman was escorted  and inserted into the line immediately in front of us. We started talking because it seemed strange and she was clearly exasperated. Turns out that she too had renounced her US citizenship years ago and on each trip back across the border was subjected to additional security screening. She felt it was punitive, but of course we had no idea if there was something else in her history that might have triggered the customs & immigration officers. In any event, she seemed quite normal and harmless and I've always wondered about it.

Good Luck Susan!