It sounds like your daughter may have inadvertanly provided her with more information that you are comfortable with. However, it also sounds like the parents of the JW girl might have been involved with the call. I cant imagine why a school girl would be interested in what congregation you use to belong to. Her mother may have suggested that she give your daughter a call and ask that question. Your daughter may have said in casual conversation that she would like to go to the meeting not realizing the gravity of your feelings or the can of worms that would follow.
In any event, these are delicate issues. Be careful not to be hard on your daughter when you talk to her. Of course it is none of my business how you handle your personal family matters. But I was the mother of two teenagers and I can say that emotions do run high at that age. Whew!! I could tell some stories.
I am sorry you are having to deal with the stress.