Complex sentence: Thereafter, she became a nun and founded the abbey of Minster-in-Sheppey, shortly afterwards moving to the double monastery at Ely, which was the precursor to Ely Cathedral, where her sister Æthelthryth was abbess.
Split into simpler sentences: Thereafter, she became a nun and founded the abbey of Minster-in-Sheppey. Shortly afterwards she moved to the double monastery at Ely, which was the precursor to Ely Cathedral, where her sister Æthelthryth was abbess.