Here's something I think strange:
If Mari's high confidence in her ability to handle Ami is justified, how come she wasn't able to shed light on her for Jiraiya? Jiraiya's
first meeting with Ami was back during the first phase of the Exams, when she hinted at the existence of the AMI. Shortly after that, he returned to Leaf and
undoubtedly discussed his Mist experiences with his Mist-born social-specialist elite jounin wife (who was not yet, at the time, broken by Hana). Yet he remained completely confused by Ami when the Tournament came.
Did Mari play a joke on him, confident that Ami wouldn't cause anything worse than a couple headaches? Or is Mari deceiving us
now?
Or... Hm. Jiraiya came back on November 21, Hana broke Mari on November 25. I suppose it is plausible, even likely, that Jiraiya just didn't get around to discussing Mist with her during that time window, and then she was in no state to advice him — leaving him completely ignorant of Ami. Very plausible indeed.