Annette Greene (TV Series)

Annette Greene was Hershel's second wife and the step-mother to Maggie. She had a son named Shawn from her previous marriage, and they both had a strong connection with Hershel and his daughter. They both later had a daughter together and named her Beth.

Hershel's Farm
Annette, along with her son Shawn, moved into the farm when she and Hershel married each other. They both presumably helped work on the farm along with the rest of the Greene family and tend to what needed to be done (caring for the livestock and whatnot).

Post-Apocalypse
Sometime after the initial outbreak, Annette was killed by walkers along with her son Shawn. Before their initial reanimation however, Hershel placed them both inside of the barn to roam freely.

Bloodletting
Shawn and her are brought up when Hershel mentions people he's lost over the course of the outbreak.

Save The Last One
Maggie relates her sadness for the death of Otis to her sadness for the deaths of Annette and Shawn. She points to pictures of each of them that are hung on the refrigerator.

Secrets
Hershel tries to insist to Dale that Annette and Shawn aren't dead but only sick and in need of a cure.

Pretty Much Dead Already
Maggie brings up Annette in a conversation with her father, reminding Hershel of her anger and depression years back when he married Annette and moved her into their house. Towards the end of the episode, Shane unlocks the doors of the barn. One of the walkers that stumbles out is Annette..

Nebraska
Annette's body is seen among the other dead walkers. A distraught Beth hovers over her step-mother's corpse unaware that she was still alive. She attacks Beth, and as the group gets the girl free from her grasp, Andrea impales Anenette through the head with a scythe. Later on, she is buried with her son, Shawn, and Sophia under some trees by the barn.

Killed By
Annette and her son were both bitten and infected by walkers when they arrived back at the farm. Over a period of time, she becomes a walker and is taken to the barn.
 * Walkers

During Shane's rampage of opening the barn, Annette comes out of the barn and is shot in the chest by Daryl with his shotgun.
 * Daryl Dixon (Zombified)

After shooting everyone in the barn, Beth runs up to her former mother not realizing that she wasn't fully killed. Her zombie mother attacks and screams at Beth as she tries to get away before Annette is impaled with a scythe by Andrea.
 * Andrea (Zombified)

Trivia

 * Hershel's wife's name was never given in the comics.
 * Herhsel never re-married in the comics after his wife's death (and as a result, his children never had a step-mother)