Hardly the point or very fair of you.
Death row conversions are a dime a dozen. Many no doubt are sincere. Many aren't. This story made the news because KFT was a pretty woman. For every one of her, there are a thousand? Ten thousand? Men who are converted on death row, and in many cases not even Solomon could judge whether that conversion is worth anything.
Deterrence and prevention of future crimes are arguments for the death penalty, but not the reason. The real reason is the biblical principle of a life for a life. When KFT took a life in the way she did her own life became forfeit. Repentence and remorse will save her soul, but it can't spare her life once that jury makes its decision.