Mary smiled the way her mother did.

我来告诉你吧。。
Mary smiled 句中缺状语。Her mother did when she was Mary’s age 句中缺宾语。即：Mary smiled (状语) Her mother did (宾语) when she was Mary’s age. 因此我们需要填一个能同时满足这两个条件的词，而这个词只能是名词。因为名词在Mary smiled 句中作状语，而名词后的句子Her mother did when she was Mary’s age 又可理解为一个省略关系代词that/which的定语从句，即：Mary smiled the way (that/which) her mother did when she was Mary’s age. 不知楼主满意不、、

原句的意思是：MARY 笑她妈妈的笑一样．意思就是她和她妈妈的笑一样． 而用as if 就是说她笑就像她妈妈在笑．前者是说他们的笑容一样。后者是说他们本身一样／

as if有假设的含义，与本意不符合
这句话的意思是 mary笑起来和她妈妈很像

as if 是好像的意思，是比喻不是对比
比如，他长的好像妈妈一样，这不是比喻 ，而是一种比较

Mary smiled just like her mother.
The way Mary smiled was just like her mother (did).

as if 好 像 就 是
She acted as if she knew everything.