You've got to understand Sarah Palin's sense of loyalty. In today's cynical world it seems a bit old fashioned, and even a bit naive, but it's a character trait that serves her well in most instances.
It's the thing that caused her to lend McCain her support in his last election, though it cost her dearly with her own supporters.
She's a smart person, and had to know the cost of giving him her endorsement, but that old fashioned sense of loyalty and keeping her word to a friend, made her do it anyway. I'm sure it's caused her lots of inner turmoil, and it would be my guess that she's prayed many times for McCain to grow a brain and to find his own loyalty to the people who elected him.
The man has betrayed her loyalty to him over and over and over again. It has to hurt, and yes, I also wonder how much more of this humiliation she can take from him before she comes right out and says, "Enough!"
What about her sense of loyalty to America? It seems that would be higher on her priority list than loyalty to McCain....