Actually, the story gets evev better! When confronted with the O-marked ballot, she also then marked it for McCain. So both zero and McCain were marked, meaning the ballot would have been disqualified. No loss for zer0, but a lost vote for McCain. Typical dem/acorn tactic!
That was probably a fall-back tactic if she was discovered. I believe she meant it as a vote for Obama but if she couldn’t get it she could plead error and get the ballot disqualified. I don’t for a moment believe this was an innocent error, especially given her violent reaction.