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Instead of actually telling her that Peace Corps == divorce, you'd be better off showing her Cary's article and then saying, "Here's the advice I got about this. I don't like this, and I really want to make this marriage work." You know, good cop/bad cop, with Cary playing the bad cop so you don't have to find one, and you get to play the good cop.
I am no fan of ultimata in relationships -- it turns salvageable situations into disasters, and even the situations where you get what you want, the other person will inevitably be resentful of the process. It may be that there is no other option than to let her go and ask for a divorce, but it also may well be that she doesn't really understand how strongly you feel about this. This column will bring that home, hopefully meaning you never actually have to issue the decree and can actually talk about it seriously instead.
Actually I think that a good amount of the time when Cary writes a column that people should just show their troubled S.O. what he wrote and talk about it. It's a good starting place for discussion, but I'm not sure you would be well-served by just following his advice in most cases.