Natalie in the final three was the fact that she didn't have her sister in the jury, whereas everybody else had a loved one in the jury. I'm actually surprised that Natalie didn't use that argument with Jaclyn (at least that I saw)...but maybe Jaclyn thought about that anyway. If Keith made it into the final three instead of Natalie, then that means that there is for sure one less vote that is up for grabs.

Now, having said that, of course it would have made much more sense from a gameplay standpoint for Jaclyn to take her chances with Keith and Missy due to the reasons you stated.