Whether the elect sin or not is irrelevant concerning their salvation, but there are temporal consequences here on earth. I have no credible information that leads me to think that Andrea Yates is/was saved (elect) so I'm not sure why you would think Protestants make such an assumption about her. We do not take profession as proof of belief.
What is so preposterous about Protestantism is that what the "elect" do on this earth simply does not matter to God. It may matter to Paul, but not to the God he created.
Of course we would say that our sinning matters to God. God says He hates sin. We have to make the distinction that post-conversion sins do not cancel the salvation of the elect because of the promises of Christ. If Christ was a liar, then those sins could cost us our salvation. But this doesn't make those sins meaningless. They have consequences and God will definitely and many times painfully discipline those He loves.
Whether you are Andrea Yates or Adolf Hitler, as long as you believe, you are as holy as it gets in God's eyes. The Big Daddy in the sky simply does not see the terrible things his little monsters are doing.
Salvation is not earned by racking up enough points by doing works. Grace through faith is what matters.
Is there a religion more narcissistic than Protestantism?
I think most Bible-believing Protestants would say that their faith is not a religion at all but rather a relationship. That is an important distinguishing characteristic.
I guess it depends on how one defines narcissism
I would say it is narcissistic to believe one can impress God enough that He would repay them by saving them
Psa 53:2 God looked down from heaven upon the children of men, to see if there were [any] that did understand, that did seek God.
Psa 53:3 Every one of them is gone back: they are altogether become filthy; [there is] none that doeth good, no, not one.