And now Sara Huckabee has joined FOX AND FRIENDS. Was this to lend more "credibility" to that show?

This is what we used to call a lateral transfer. 
Is it possible to have a mutually detrimental relationship? 

What’s funny, is compared to the other mutants on that show, SHS in an “insider”. 

I think they just needed a sour puss they already have their yellers and conspiracy spreaders  so they needed somebody to look ominous. It was also to add credibility to the show - Sara can say things like you know I have worked with the president so I can assure you that's not what he meant or other things like that.  Cheers and happy weekend!

She is not joining Fox and Friends. She will simply be a political commentator.

maybe

I marvel at her uncanny ability to look at two sides of things at once
due to that lazy eye.

One looks right.  One looks left.
That could be an asset when it comes to various topics.