After she gutted the walker attacking her, his instestines and blood spilled onto her. This covered here in "walker scent" and she could walk freely among them. Operates the same as her "pets" she had. They masked her "living" scent with their rotting smell. Rick and Glenn did the same thing in the first season to help the group escape from Atlanta.
But I would worry about the walker blood infecting her wound.
Ah, it all makes sense now! Thanks. The 'guts scene' completely slipped my mind. I guess I've also sort of become desensitized because it seems like people are constantly getting splashed with walker juices...lol