I bet she did it just to please her constituents. If she had the slightest feeling it might be in danger of not passing, she would have voted for it. Instead, she knew more than enough Congresspeople would vote for it to pass, so she probably did it for publicity reasons.
By the way, thank you to Marcy Kapture, Dennis Kucinich and Walter Jones. All of them have been consistent in opposing the Patriot Act alongside Ron Paul since day 1.