That certainly has been the pattern but if she doesn't want to be shaking her finger in the face of the next president, she will not endorse Romney.
Shell pick Romney because she needs the Mormon votes for her next and final election, who will desert her in droves if she endorses any non-Mormon.
Yes, there are a lot of Mormons in AZ but they aren't the majority.
Then too McCain has endorsed Mitt so he might have told Brewer to tow the party line.
You are correct, they are not the majority. But they are a voting bloc large enough they can't be ignored, at least on the Republican side. I would bet they will vote Mott at a 95% rate, and they are sizable.