Complex sentence: She has one child, a son, Alan, by her first marriage, who is also a singer, known professionally as Alan Merrill best known as singer and songwriter of the original 1975 version of the rock classic "I Love Rock N Roll".
Split into simpler sentences: She has one child, known professionally as Alan Merrill, by her first marriage. A singer, he is a singer and songwriter, who wrote the original (1975) version of the rock classic "I Love Rock N Roll".