Your difficulty with comprehension may lie in the fact that you have missed the "on" from the quoted passage. I would interpret the passage as meaning that the young lady in question had achieved somewhat more at high school than simply having sexual intercourse on the [presumably secluded] fire escape stairs.
You said some time ago that you were seeking to gain insights into certain aspects of Society through this book. From the passages quoted so far, I would guess that the only insights to be gained might be to the fevered imagination of the Author.
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