The teacher of their mother Fu is first tier, and his student after learning for years and then send to China is second tier, she must have learn most level and have master higher level may be six or seven before she is consider good enough to be sent to China to assassinate the emperor.
The first tier are grand master and big boss, the second tier are good enough to led an army, see her rival Yumen, Sung, Du, Dai Lung Tau etc.