So you are trying to wack your MIL? That is cool. What does your hubby say about the JW? DOes he think they are the one true religion?
THe advice you got was "quick". There is nothing quick about opening a closed mind.
I would recommend reading some books about cults before you really try to make a run at her. If you approach it like you are trying to win an argument, then you have already failed. Talk to them like a person, not a salesman. Real people actually care and are interested in the person. Salesman only are interested in the person as it pertains to making the sale. Get the difference?
Maybe order Combatting Cult Mind Control and/or Releasing the Bonds both by Steven Hassan.
His whole deal is that helping someone out of a cult isn't a matter of this info or that. It is more of a process. It also might be good for your hubby to read these books as well. Even if he is not in, it might be healthy for him to read about mind control and the phobias that are used to keep people captive.
You might help to clear up some of that "waffleiness".
See the JW are a cult not because of what they believe, rather because of HOW THEY BEHAVE!!!
If someone has the truth they should never have to threaten people with shunning or demand that people not read certain books. Those are control mechanisms to limit a persons perspective to the cult perspective.
Ask your husband how he would feel about it first. If it would bother him read them on your own and maybe mention some of the ideas to him. If your MIL has other family that IS NOT jw, see if any of them would be interested.