In the first article I read (http://www.sptimes.com/2008/01/22/Northpinellas/Flip_side_is_told_in_.shtml" from the St. Petersburg Times) the police officer said that she approached him with fists clenched (which may be construed as threatening), and refused to move for 20 minutes or so after being asked (illegally detaining the police officer, since he couldn't move his vehicle).
The McDonald's manager backed the officer's version of events. Another witness seems to back the woman later in the article, but left before things escalated and admits that the police officer was upset because he was unable to move his car because of her car blocking it. So her best witness doesn't really help her as there is no right to prevent others from leaving when they ask a person to move.
A young man walking toward an officer with fists clenched, refusing to follow a lawful order to not trap the police officer's car after being repeatedly asked not to do so for 20 minutes would be arrested. It was right that she was, too.
I might add that blocking a drive thru for 20 minutes probably caused a large loss of revenue for that business. There were some very unhappy customers lined up behind and possibly trapped there, as well. I think trying to reason with her for 20 minutes was generous. Had the police not arrested her, how long would she have stayed there?