I would let them have their JW thing at the hall or funeral home, especially if that was want you think she wanted.
Then, have your own thing for family and friends. I would let the JW siblings know, and even have someone pass the word around to those that were he JW friends...they would probly enjoy listening about your mom, and not just the standard talk.
That is exactly what I will do when my mother passes away (wow, this is one of the few times I did not write if instead of when). I am sure there will be several witnesses at both services for her.