Complex sentence: She is best remembered for her association with the composer George Frideric Handel, whom she sung for at both Italy and London, though she also sang in operas by Alessandro Scarlatti and Giovanni Bononcini.
Split into simpler sentences: She is best remembered for her association with the composer George Frideric Handel, for whom she sang both in Italy and in London. As well as singing for Handel, she also sang in operas by Alessandro Scarlatti and Giovanni Bononcini.