Alternator, I don't have much advice to offer you that hasn't already been said. You're in the position I have dreaded: having a loved one risk her life for the sake of Watchtower treachings. For my (now Ex) wife I probably would have made the same decision you did: allowing her, as an adult, to make a decision that I find reprehensible. But for our minor children, I could never allow their lives to be risked as a WT loyalty test.
I hope you have consulted your own pastor for guidance on dealing with this. Since you have said that you are Catholic, consider articles 2280 and 2282 of the Catechism and how they relate to this situation: are you being pressured to cooperate with a suicide, a willful refusal to protect one's own life? That is why I mention getting advice from the clergy.
I hope all goes well for your wife, despite the medical teachings of the Witch Doctor Society. Please let us know how things turn out.
GLT