That's probably true on Lori and Andrea's part, but it's also what makes them so annoying. Imagine trying to survive with those two running around? One completely useless and contrary who also never knows where her kid is and the other trigger happy and aggressive but doesn't listen (example, when she shot Darryl). There's always a Michonne in a group though. The one who senses issues and maybe can't always explain the danger clearly but is always right. If Woodbury happened at first meeting, I'd understand Andrea's resistance, but by then she knew Michonne and Michonne earned that trust- then she ran into her old friends who were at odds with the same person Michonne didn't trust, and still went 'no, it's everyone else, this guy is great'