Complex sentence: This flattery spoiled her, and she began to believe herself queen; she passed Queen Marie Thérèse without greeting, and treated Athénaïs de Montespan ignominiously.
Split into simpler sentences: This flattery spoiled her, and she began to consider herself as the Queen. She begun passing by Queen Marie Thérèse without greeting her, and treated Athénaïs de Montespan ignominiously.