Because I don't think she was that great of a candidate. She wasn't seen as significantly better than the other two. I'm not surprised she's finishing third. Palin may have helped her a little, getting her from 25% to 29%. Maybe.
The voter turnout for the Dems was low maybe the open primary invited them to sway the outcome to who Claire wanted to run against and at the same time make Palin look like a loser by sabotaging her candidate. Open primaries are the Devil’s tool and they have always watered down to party vote with people who have no right picking the Republican.