Complex sentence: Lucy had taught at UC-Berkeley for only two year, but then her declining health, always frail, led her to return to Boston, where she passed away at the end of 1920, at the age of 53.
Split into simpler sentences: Lucy had taught at UC-Berkeley for only two years. But then her declining health, always frail, led her to return to Boston, and she passed away there at the end of 1920, at the age of 53.