Yes, there are times when someone is out to get you. It doesn't happen that often though. Instead, external letters are data points that help you evaluate a file, especially when you don't know much about the field. In this case, Jenny is in American Politics so half the department already knew she was not interested in research. For better or worse, that just won't cut it come tenure time. She was delusional to think that Kentucky would matter in the second go round. A co-authored book with your advisor, too, c'mon.
My guess is that the favorable reviews of her work are all from friends. She chooses 3 most likely. Her advisor had friends, and she's friendly to some as well. When you bias the fact that reviewers do NOT want to write bad letters, those letters of advocacy really aren't that great. Add the negative, which was truthful if you read it, and that's a no-brainier tenure denial.