A couple problems with the analogy.
-- Eva Peron never ran for public office, and only held an appointive one (as head of Fundacíon Eva Peron.
-- Fernandez, Royal and Clinton have run for office, and have political experience in their own right.
-- It's a cheap shot to speak of Royal as a "common law wife". Common law has to do with the Anglo-Saxon legal system, not Napoleónic Code.
Evita was poised to take the presidency and could reasonably be said to be likely to have gotten it had not cancer intervened first. Only death prevented her from becoming president. Isabelita made president, for a time at least, and was appointed. Evita most certainly "ran" for office if you know anything about Argentine politics. The point is this: If there were no Juan, there'd be no Evita. If there were no Bill, there would be no Hillary. If there were no whatsisname, there would be no Sego, if there were no Nestor, there'd be no Cristina. All came prepackaged and a pretty one at that, courtesy of their husbands and their power and their political machines.
What's your problem with 'common law wife' - it describes something, doesn't it? Perhaps you prefer the franker 'shackup'? Or 'unwed mother'? That's what Sego is, for your information. No society can sustain itself on unwed motherhood that you seem to think is embedded in Napoleonic law. Guess what, it isn't.