Complex sentence: She may have assembled a collection of writings and music, the Ledenburg Collection from the manor house where she was born, which held music by notable 18th-century composers that seemed lost until it was rediscovered in 2015.
Split into simpler sentences: She may have assembled a collection of writings and music, the Ledenburg Collection from the manor house where she was born. The collection held music by notable 18th-century composers that seemed lost until it was rediscovered in 2015.