The media is going to focus on Pippa because they think people want to read about her. The Facebook page, the clicks on articles about her, the yahoo search numbers, etc. Its all about numbers.
That and she is not an unattractive girl, there is an interest in Kate (and her family), etc. Plus, Kate is not available right now, and its easy to focus on someone they see out and about.
Hopefully, they will start to back away and let the girl have some room. If not, the backlash should start hitting in a couple of minutes. You know how some in the press like to build a person up, so that they can tear them down. Already posters in the DM are wondering why the press is following her.