Complex sentence: Miss Minchin throws Sara a lavish birthday party in order to extract more money from Captain Crewe, but when word comes that her he was killed in battle and his estate has been seized by the British government, she forces Sara to become a servant.
Split into simpler sentences: Miss Minchin throws Sara a lavish birthday party in order to extract more money from Captain Crewe. However, when word comes that Captain Crewe has been killed in battle and his estate has been seized by the British government, she forces Sara to become a servant.