Complex sentence: Kain began training in 1962 at the age of eleven at the National Ballet School of Canada, where she trained for seven years until upon graduation in 1969, she was invited to join the National Ballet of Canada.
Split into simpler sentences: Kain began training in 1962 at the age of eleven at the National Ballet School of Canada, where she tained seven years. Upon graduation in 1969, she was invited to join the National Ballet of Canada.