She would have won, but it would have been by around 3-4%. I think the slump for Obama/Landrieu would have been similar in the rural areas regardless, but Obama really helped to turnout blacks for her in Baton Rouge and Shreveport.
Keep in mind, Katrina recovery was still a huge issue then. Lots of ordinarily-GOP suburban New Orleans voters were willing to look past her party label becuase of her recovery efforts. I think they would have done so even in normal/slightly Democratic year.
Yeah, Louisiana's incumbent-friendly in congressional races (not so much in state races). And just three years after Katrina, the seniority argument (and plus everyone knew she'd be in the majority party then) may have carried some weight.