Why didn't Michonne simply tell Rick and company that she was with Andrea? She obviously knew who they were once she met them at the prison. There is no way she spent almost a year with Andrea and didn't learn everything there was to know about Glenn, Rick, Carole, Daryl etc. She would have to be extremely slow not to connect two identical groups of survivors at the end of the world with the same names...
Also why did no one from Rick's group ask Michonne why she was so eager to go back to Woodbury? Did I miss somewhere that she stated she had someone there "she" needed to rescue? I can't imagine given the nature of the world that people go out of their way to risk themselves just for the heck of it. Sure she got shot and might want revenge, but helping to take on a heavily armed, fortified town?
Couldn't Rick have at least asked her why she wanted to go back?
I assume they want to drive up the suspense in the inevitable confrontation involving Andrea and Merle but seriously do we have to suspend that much disbelief?
Also I'm calling it now, Merle is going to turn against the Governor. He may like his new life and position there but he will not let the Governor take out his brother. In fact I bet he helps Glenn and Maggie escape. He's a bad guy but he won't risk the loss of his brother.
Zombies in the prison... again? Doesn't matter what the Woodbury soldiers to to drive zombies in, a prison is heavily fortified from within and without. All the group has to do is lock the doors on their cell block and wait for Rick and group to return.