Complex sentence: After the death of her son, Isabelle spent every summer in her duchy of Alençon and most winters at the royal court; she would sometimes stay in Paris at the Luxembourg Palace which had been ceded to her after her mother's death in 1672.
Split into simpler sentences: After the death of her son, Isabelle spent every summer in her duchy of Alençon and most winters at the royal court. When in Paris, she would stay at the Luxembourg Palace which had been ceded to her after her mother's death in 1672.