All well and good
However, this type of situations often include the victim not being able to stand up to the abusive treatment, and having to obey orders. So short of making it impossible foranybody to install a tracing app — not even the victim — I'm not sure what technological solution there is.
As the authors themselves note, there are legitimate uses, and no good way to make distinctions.
They might as well ask video camera makers what they do to protect the privacy of people.