Complex sentence: Harmon Tupper died in 1988 and Elsie remained in Nantucket until her own death, bequeathing her estate to the Nantucket Atheneum library.
Split into simpler sentences: Harmon Tupper died in 1988 and Elsie remained in Nantucket for the remainder of her life. Upon Elsie's death, she bequeathed her estate to the Nantucket Atheneum library.