Hama in my opinion was just a woman driven mad with grief over the loss of her family and friends. She was friends with Kanna (Gran Gran), which leads me to believe that her interest in Katara wasn't solely to teach the young waterbender bloodbending. She probably felt a slight connection to her, realizing that Katara bore a strong resemblence to her best childhood friend.
These reasons make me believe that Hama wasn't just out to kill for no reason, she was simply grieving the loss of friends, and her time in the Fire Nation prison simply helped to make her angry enough to seem crazy.
Any other thoughts on Hama?
