Unlike an interrogation, the author could have stopped this ordeal at any time by turning off or simply not answering her phone.
On another occasion feds came to my house to investigate a neighbor. When I refused to talk they waited until I was shutting the door and stuck their fingers in to try and get me for assault as it closed. Thankfully I caught the door at the last millisecond and just stared at them blankly with the door cracked until they left.
Getting rid of qualified immunity for most law enforcement agents would be a good start.
This is a (mostly) effective way of immediately stopping an interrogation.
Yes, a police interrogation is even more intense than what the author experienced. But confessing to murder is also quite a bit more serious than handing somebody 50 grand in a box.