Her CFII said another CFI told him that "she struggled with the radios, and it was one reason why it took her so long to get her private. It took over 180 hours to get her private." What's more, he further stated that "he would take over the radios so she could focus on the flying." This was among many other deficiencies. Considering that he trained with her AFTER she received her private pilot certificate and in the same accident aircraft, one can assume that he provided the high performance/complex training and logically the endorsements.
I can't help to read this over and over and still left with so many questions... Flight Instructor Interview:
https://data.ntsb.gov/Docket/Document/docBLOB?ID=19961280&FileExtension=pdf&FileName=MOR Flight Instructor Interview_Redacted-Rel-Rel.pdf
While I believe whole-heatedly this fatal accident was TNFlyGirl's fault without question, I also think about how any CFI could sleep at night having signed off on anyone with such deficiencies.
I once had to fire a CFII during my private training. He was eager to fly, but I had said it was a no-go due to the weather. He insisted, explaining that the airfield was Class E and that we could fly on top of the clouds to another airfield to do pattern work. Since I was new at the time, I agreed—after all, he was a CFII. Once we got on top, there was no visible hole in the clouds, though maybe 20 miles away there might have been one. We pressed on. An hour later, he decided it was time to head back. He circled the airfield for nearly 20 minutes, burning time while waiting for a break in the clouds. Eventually, he found a hole, dove through it, and landed. If we had needed to go around, there was no way we could have done it without going through clouds. After landing, we debriefed, and I excused myself to use the restroom. While there, I found the chief, explained the situation, and told him I would never fly with that instructor again. I never saw that CFI at the flight school after that.