Given that Landrieu has won two runoffs in the past, I'm guessing that she's not in the hideous shape that some people think she's in.
Louisiana has gone farther to the right, Obama is deeply unpopular, and the race would be heavily nationalized in a runoff, especially if Senate control is up for grabs. She may be a skilled politician, but this is going to be an environment unlike what she has faced in past elections.
And all of these things aren't already variables? I'm not an expert on LA demography or turnout, but something tells me that natural run-off turnout when compared to the general isn't as contrasting as it might be in, say, my own state - or at the very least, isn't as disadvantageous to Democrats.