I think it depends about the person you're talking to.
For me, doctrinal stuff probably would have worked best. (It's what eventually woke me up.)
For my wife, it was the child abuse things she couldn't excuse. Specifically that branch representative stating that the congregation's "protection was a spiritual protection" not a physical one.
I think it's different for everyone.
Perhaps lay some groundwork before you ask her for the 5 minutes. Innocently ask her, "If there was one thing you could change about Jehovah's Witnesses, what would it be?" That might give you a clue as to what part of the organization's policies she's sensitive to. In fact, she may even ask YOU what you wish could change. It might open up a good dialog.