I think there are a lot of areas to expose, Mary. I would recommend finding a micro as opposed to macro here. Then try and keep it focused [good luck with Jdubs].
Here's one - open your Bible [they like that] to Romans 13. Ask her to read it and explain who the 'superior authorities' are in those verses. Then ask her, if she were 15 years old, and had never read the verses before, who would it seem the 'superior authorities' were in those verses. Her answer will be the same both times - and she will wonder where you are going with this. Then show her society quotes that show for how many years, the "Organization that Jehovah is using to direct his people" had it wrong. And that 'under the direction of Holy Spirit'. And then that same wishy-washy Holy Spirit finally saw it clearly, like the 15 year old, that they had it wrong for all those years. No reason that the Holy Spirit would have mis-directed this matter for all those years. The other religions had it right during all that time - why not the 'TRUTH'?
It is not an argument that will turn her out on one discussion. But it was always something that made me wonder. Doubts are the key here.
Just my opinion
Jeff