各位好，请教一下
在朗文辞典看这样的例句：https://www.ldoceonline.com/dictionary/back
She was the one who had fired him from his first job back in South Africa.
为何这句子后面要用过去完成式had fired呢？应该也可以只用过去式吧？如：
She was the one who fired him from his first job back in South Africa
过去式就可以表达了，想不出要用过去完成式的理由。后来我试着想像一个语境：
(She told me that) She was the one who had fired him from his first job back
in South Africa.
这样对我来说，用过去完成式就合理了。
“她告诉我”发生在过去，而“她在他第一份工作时开除他”发生在“她告诉我”之前，
也就是“过去的过去”，因此用过去完成式。
不晓得我用这个方式理解可以吗？有张贴在英语讨论区https://goo.gl/vHzdHK，
不过还没有人回应，那边如有回应会再贴回来和大家讨论。谢谢！