Complex sentence: Spanish-language networks in the U.S. often broadcast documentaries about Selena on the anniversary of her death; they are among the most-watched programs in the history of American television and often score record ratings for networks.
Split into simpler sentences: Spanish-language networks often air documentaries about Selena on the anniversary of her death. They are among the most-watched programs in the history of American television, and often score record ratings for networks.