She was a total anomaly in a district that had been Republican for 70 years. She won because,
a)Obama fever
b)Secretary of State Brunner was an ACORN operative
c)Manipulated three recounts to "win" by less than 1200 votes out of 400,000 cast.
She then proceeded to vote 100% with Pelosi. Even some Democrats were furious at that point. In 2010, she had her rear end handed to her. She blamed her loss on the "racist" Tea Party.
I’m not sure of the total count here, but Giffords barely won with 4K of the votes. Kelly actually won election day (with 54 or 56% of the votes, I forget), but because Giffords had refused to debate until after the early ballot deadline, those people bought into her commercials (with full-fledged lies about Kelly).
There are many other reasons... including how of course we evil horrible white racist Christian OLD tea partiers were so mean to her and made her cry at the townhalls she finally held.