She was covered in zombie guts from the one she sliced open previously.
S01E02 showed this when Glen and Rick walked through the streets of Atlanta to get the truck, covered in guts. The walkers didn’t notice them...until it rained and started washing the stank away.
Thanks.
She looked confused when they walked right by her - guess we just took her look the wrong way.
At any rate, her suspicions about Merl, The Gov., etc. were pretty much confirmed when she watched Merl take Maggie and Glenn away at gunpoint. She doesn’t seem like the sort to just let something like that go...