Complex sentence: She participated in the fight against the Spanish Armada, and during the Earl of Essex' 1596 Azores expedition she served as the ship of his second in command, Sir Gilly Merick.
Split into simpler sentences: She participated in the fight against the Spanish Armada. During the Earl of Essex's 1596 Azores expedition she served as the ship of his second in command, Sir Gilly Merick.