Andrea was tied up in Woodbury as we entered The Walking Dead Season 3 finale — Episode 16, "Welcome to the Tombs." The Governor stabbed Milton, then put him in the room with the tied-up Andrea so he could turn into a walker and bite her. Milton gave Andrea some pliers, but she took too long to get herself free. She was bitten. Team Prison found her as she was still alive. She and Michonne had a last moment together before Andrea was shot.
Andrea had a tough time on TWD Season 3. Her character, who is still alive in the comic book series, went on a very different journey. Fans turned against Andrea this season when she fell in love with The Governor, and chose to stay in Woodbury rather than leave with Michonne. She had opportunities to kill The Gov but, as she explained to Milton, she just didn't want anyone to die. She's the anti-Governor and the anti-Carl — they have shown they're not afraid to kill everyone.
Are you upset that Andrea died? Do you wish she had killed The Governor? Do you wish SOMEONE did?