This article about a student's nightmare internship details some of the same attacks that are used at my job.
1- The supervisor said that she had never seen the intern do any work. The implication is that the intern does no work. When the intern pressed the supervisor to explain, she denied any wrongdoing, explaining that she had never seen her work with a client because she never observed her in the private counseling room and had no intentions of doing so.
People do this at my job all the time. They report, "I did not see So-and-So doing that" to convey that the task was not done. When confronted, they will justify the answer with "I was not in the room when you did that, so I did not see you." However, when spreading rumors, not being in the room and not witnessing an act does not disqualify someone from asserting its truthfulness.
The other shade of this technique is to say, "I don't know where So-and-So is," implying that the person is missing from an assigned work station without permission. When confronted, the instigator will reply, "I know you said you were escorting a patient. But I was not with you, so how would I know where you were?" And no, they can't say, "So-and-So left ten minutes ago to escort a patient." They have to make trouble.
2- The supervisor accused the intern of not being successful in patient care. When the intern showed evidence of her effectiveness, the supervisor explained that any success was do to the intern's improper behavior with clients and not because she is a good therapist.
At my job, other employees get upset and angry if they see that I have a positive rapport with patients. They accuse me of buying cooperation from patients with money, gifts, or flirtation. They can't accept that treating patients as human beings would positively impact behavior.