Complex sentence: She is best remembered as an early patron of and sympathiser with the youthful Metastasio, whose work she encouraged and helped to develop, but she was also a popular and successful singer of "opera seria", renowned for her acting ability in particular.
Split into simpler sentences: She is best remembered as an early patron of, and sympathizer with, the youthful Metastasio, whose work she encouraged and helped to develop. She was also a popular and successful singer of "opera seria", renowned for her acting ability in particular.