Complex sentence: The highly controversial marriage proved barren and after his death and the accession of her stepson Theophilus she again retired; however, she does appear to have been responsible for Theophilus's marriage to Theodora, who helped restore the veneration of icons in the empire.
Split into simpler sentences: The highly controversial marriage proved barren and after his death and the accession of her stepson Theophilus she again retired. However, she does appear to have been responsible for Theophilus's marriage to Theodora, who helped restore the veneration of icons in the empire.