Complex sentence: The importance of Bonnin for American Indian grand opera cannot be underestimated, considering that few if any American Indian operas on American Indian themes, using indigenous performers, have been composed by American Indian composers since her era.
Split into simpler sentences: The importance of Bonnin for American Indian grand opera cannot be underestimated. Few if any American Indian operas on American Indian themes, using indigenous performers, have been composed by American Indian composers since her era.