Complex sentence: She began to pursue a singing career in earnest at age 16, when her father's health began to decline; he took Shemekia on tour as his opening act, which helped establish her name on the blues circuit.
Split into simpler sentences: She began to pursue a singing career in earnest at age 16. When her father's health began to decline, he took Shemekia on tour as his opening act, which helped establish her name on the blues circuit.