You are right not to directly attack the WTS. It is possible, however, to get Dubs to exercise their minds by attacking the ideas and practices of another cult. For example, reading Combatting Cult Mind Control, by former Moonie elder Steven Hassan, would allow you to discuss the Moonie cult in a way that is non-threatening to JW’s. Not only will she happily condemn the Moonies for their practices, but also, if you’re lucky, she might see the connection for herself between the two groups.
Best of luck,
Mr Ben