这个空要填 that
in the way that her mother did at that age.
和她妈妈在同一年龄时后那样地笑
that 引导从句 that her mother did at that age 修饰 way
顺便一提,这种句型 that 很常被省略.
我是加拿大人,前英语老师.所以是定语从句吗？是的。