Theresa was a thinker first before being a fighter. She was the brains whereas her sister was the brawn. She was the one who made sure to read all the clauses of the contract to avoid having her sister sell herself out without knowing how she even did that. Her sister was a natural klutz when it came to these things so she thought of it as her job to take care of them in her stead.
This didn't really mean that Cecilia was a stupid woman. No dumb person could reach the heights she had reached in her life. Theresa's sister was not stupid or dumb, she just did not like thinking as she could resolve most if not all solutions with her fists and muscles alone.
Theresa though, while extremely talented in her own right, was just your average genius. Unlike her sister and Mei who were monsters.