This is just nonsense. The dictionary definition is not a nuanced and proper understanding of human behaviour or moral thought. This is the definition of to steal:
steal. to take (the property of another or others) without permission or right, especially secretly or by force: A pickpocket stole his watch. to appropriate (ideas, credit, words, etc.) without right or acknowledgment.
If we were having a discussion on the issues surrounding stealing, we couldn't use this definition alone to get to the bottom of what is and isn't stealing, how stealing should be viewed, and so on.
So, in fact, your point of view is that anyone who even in the slightest fails to live up to their beliefs is a hypocrite. There is some truth here in the minor sense of all men failing to live up to the standards they set, but generally we reserve hypocrite for egregious cases. Anyway, if what you say were correct full stop, then it wouldn't make sense to single out this woman. If almost all men are hypocrites, then why single out Kim Davis as one?
Well, we don't know she hasn't. A lot of the claims against her rely on her divorces being immoral according to her beliefs. This is not necessarily the case.
But, more generally, what you say just doesn't seem apparent. Why can't someone who has sinned still believe and advocate for what they believe in? She presumably still feels it is right. If she were holding herself out as perfect or looking down on others for what she herself has done, that would be different, but it is not apparent to me that one cannot stand up for a position if one is not perfect.
There also seems to be an excessive focus on the her person here, compared to the ideal, as if her actions tarnished the ideal. If one held the older view that ideal was something men rise to or fall away from, but which is ever unchanged, then it makes even less sense to suggest that by falling away from it, one should then abandon it and never advocate for it.
Ultimately, hypocrisy, in the proper, egregious sense, is not about failing to live up to our beliefs alone. It is about pretense, as your own definition said. It is about pretending we are perfect or better than others.