Oftim is a minor character in the TV series. She is a Handmaid and presumably was trained at the Rachel and Leah Center. At some point during either her training or her time as a Handmaid, she had her right hand cut off.
In the Present Edit
One of the punishments women can be subjected to in the Republic of Gilead is the removal of a hand for being caught reading twice (once being punished with the loss of a finger). Since Oftim is missing a hand, it is possible that she was caught reading on more than one occasion at either the Center or in the household she is assigned to.