Presidency of the Texas State Bar is not an award given to the best lawyer in the State of Texas. It is the culmination of years of glad-handing and back-slapping (with a dash of tokenism) in a mutual admiration society. Texas State Bar elections are most akin to the old Soviet elections. The ruling claque selects two candidates (who in certain years meet either a gender or a minority requirement) and then the hoi polloi can select among the chosen two.
As a caveat, I think I did vote for Ms. Miers (in one of the last years before I stopped voting in State Bar elections) because she was only a mushy mod-liberal while her chosen opponent was a hard-core liberal.
Not merely that she was president of the association, but that she was the first woman to hold that post.
She is a poster child for women's equal rights. The WH is playing to the female wing of its support constituency (as well as the evangelical wing and party-faithful wing). Of course, there is some overlap in those constituency groups, and none of them are "all in" or "all out."