Her insight: A witness often wants to win the approval of the lawyer prepping her to testify. There is a power disparity, not unlike a child and a parent.
There is a lot of truth in what she says. I recall witnesses who brightened when I told them “good job” but who darkened when I offered even the gentlest feedback. Neither manifestation of the dynamic is useful to the task of telling the client's story in the most effective way possible.
What is an astute lawyer to do? Develop a message system with witnesses: Ask them what they want the judge and jury to understand about the case. When preparation is finished, ask them a simple question: “Do you feel good about our message, or are we leaving something out?”
Make the witness prep about collaboration and a goal, not about hierarchy and dis/approval.