She had finally achieved what she had set out to do, which was make her son ascend the throne.

set 的基本意思是"放置、设定"，在这里与 out 搭配使用。 out 在这里表示"向外、开始"的意思，与 set 搭配构成短语动词。 set out 这个短语动词的意思是"开始着手做某事"或"设定目标"，表示开始某项任务或计划。