The point there was there was no detail too small to leverage. They depended on huge amounts of people feeling as if they had no choice but to inform on their families, neighbors, and co-workers.
In the movie, this particular woman was leveraged in just that way because they had her over that barrel, and let her know explicitly that was the expectation, IIRC.
Spent 2 years being tracked by the Stazi. I knew them well.