My wife is Brazilian and has a large family in Brazil.. I completely understand the difficulties that a tight family can pose.
What I can recommend is, don't try and prove the society wrong, rather prove the Bible right.. Many people get caught up in fleshly thinking, and they judge the organization for its actions..
Show her how the witnesses rejoice that all "worldly" people will die at Armageddon, and ask her if this is Love. Show her that even the sodomites will be resurrected.
This is one apology that can make some think..
The Israelites were Gods chosen "organization".. If you were an Israelite, you would have NO DOUBT that Jehovah had chosen the nation as his people, he gave many signs and miracles to prove it. Now if you were an Israelite, and you saw one of your "governing body" members assisting in the building of a calf for false worship, would you be excused at judgement day if you followed the lead? Exodus 32
tie-in Galatians 1:8'- But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let them be under God's curse!
It can be a VERY TOUGH journey if she is one that doesn't know the bible and she doesn't know the org.. You can overcome it though.
Try your hardest to keep your marriage in tact.
My wife and I would like to help you, and we can assist you in Portuguese. PM me if we can help.
With Christian Love