Complex sentence: Christina Anna was no passive partner to her brother and spouse: she was present in person in 1663, when they attacked a Dutch merchant ship, murdered its crew and sunk the ship somewhere between Öland and Bornholm.
Split into simpler sentences: Christina Anna was no passive partner to her brother and spouse. She was reportedly herself present in person in 1663, when they attacked a Dutch merchant ship, murdered its crew and sunk the ship somewhere between Öland and Bornholm.