>>>>Given this persons situation, why can't his wife be officially charged, tried and sent to prison for "Conspiracy" to commit murder?
Conspiracy requires, at least, an agreement between two people. Here, she has been "talking" about it only amounts to coulda/woulda/shoulda. However, prior to a conspiracy, she would have to solicit someone and that, by itself, constitutes a crime and is much easier to prove. But, still, it takes two to tango . . .
Also, as far as her threats, they do not constitute an "imminent" harm so whatever assault statutes exist probably have not been violated. Now, if she were to say something directly to the OP about killing him "right then and there" and had the present ability to carry out the threat, that type of threat [at least in CA] would be a pretty serious felony and would also constitute a strike.