Black sheep, Of course it matters!
This young person may lose their perspective on life and waste their life pursueing promises that are worthlesss, and you may be in a position to help her.
As the borg used to say "Knowlege brings responsibility" and people like us have that resposibility to speak up and not let the WT nonsense be passed on unchallenged.
I agree that a blunt frontal attack may be unproductive , both to your marriage and this girls studying . After all, the first thing they learn is to expect persecution. A softly softly approach may be better . You have to encourage her to check out all sources and not take all they say at face value. Once she finds one falsehood, the rest may unravel.
I spoke to a young lady at work who was having regular return calls from the dubs. The thing that made her stop was when she found that the NWT did not accord with other bibles. You never know what will strike home.
BTW my wife is also an active dub - it is not an easy tightrope to walk, is it ?
Best wishes.