Teresa was vastly underutilized as a number 1. She was sent to a town to kill seven yoma. In most of the manga, we see that single digits are sent on unusual missions, like investigating large groups of Yoma collecting, or awakened being hunts. We don't see Teresa leading teams or meeting other claymores (aside from her death squad) in the time she knew Clare.
When Ilene, Sophia, Noel and Priscilla meet up in the Yoma town, it's mentioned that any one of them could've handled the town on their own. If anyone from the top five could handle a town of Yoma, why send Teresa for seven yoma? I think at that point it wasn't known if it was seven yoma or if it was an awakened being. On Clare's first mission with Miria, Miria considered that an awakened being could've been close by. Clearly, the missions Teresa was assigned was way below her ability. It's only the execution of Rosemary that was suited to her ability.