Here is my real dilemma, how do I stay her good friend without becoming a JW?
I hate to tell you this, but you can't. Once she realizes that you don't want to sign up she will begin to limit her association with you until finally you rarely see her. That is what cults do.
I know it's a raw deal, imagine if she were your mother or blood sister? Many of us here have suffered through the total emotional loss of very close family members due to this religion. It sucks.
My advice is to resign yourself to finding a new friend.