Maybe I misunderstood your post a bit, but personally I dont go around picking fights about such things. I'd wait until they try to preach to you about some silly crap and then try to point out the flaws in it.
Oh never! This drama is all playing out on another discussion board and I only chime in when the JW starts spewing twisted rhetoric. Other people on the board don't get why I care, and some are regular 'Christians' who come to her defense (that is til I posted how JW's believe all non-JW's...including "Christians" will perish at Armaggedon).
I think I'll stick with Gary's advice and not try to reason with her (actually I post for the benefit of the civilians who might buy into the JW stuff)