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My advice is not as drastic as some others here. My advice is for you to be the best friend you can be to this person. You'll need to understand that her religion keeps her away at times, but try to make her feel OK about that.
I think it is great when JW kids meet kids from other religions at school. This shows these children how much of a lie they are being taught about worldly people. Its hard for a witness kid to have friends that they know are nice, and then attend the meetings at the Kindom Hall and hear talks about how bad the world is. This may be one of the things that helps open their eyes.
Be careful how you talk to your friend about religion. Don't critisize her religion. If she asks you to attend the Kingdom Hall, decline and invite her to your church. She won't accept your invitation but it might keep her from trying to convert you.