Michelle is a minor antagonist in The Walking Dead Season 2. She is responsible for Omid's death and is a cold hearted bully.
Nothing is known about Michelle's life before or as the outbreak began.
When Clementine went to the bathroom, Michelle wasn't far behind and managed to follow here there. When Clementine drops her bottle of water accidentally under the bathroom stall, Michelle comes in and steals her gun. Michelle found out she was in the stall and began threatening her, ordering her to get out. She searched through her bag while holding Clementine at gunpoint, keeping on threatening and insulting her. She complained her limited amount of supplies but didn't buy the fact and ordered her to take off her hat. She eventually finds a picture of Lee and ruthlessly called him a bozo. She also named Clementine a "little fish".
Omid sneaks into the bathroom and heard about this, carefully trying to subdue Michelle and take the gun off her to save Clementine. Though Michelle heard him, panicked and shot Omid dead. Christa came in with a Rifle and found Omid dead with Michelle as the murderer. Michelle dropped the gun and raised her hands in surrender, trying to convince her to spare her life, but Christa shot Michelle in the abdomen in sorrow, killing her.
Michelle is a ruthless and cold bully who seems to hide her fear through a hurtful exterior. She also didn't care that Clementine was just a kid and continued to say heartless things to her and even held her at gunpoint. She seemed to care only for herself and shown what she's really like when she killed Omid when she panicked as Christa arrived. Michelle is possibly not a killer as she seemed generally shocked that she had killed Omid and was likely sorry for it as she had stated. On the other hand she could've just been afraid for her own saftey.