Among them will be Debbie’s mother,who swam the Channel hers

Among them will be Debbie's mother,who swam the Channel herself when she was a girl.
这句话的意思是：他们当中还会有戴比的母亲,当黛比的母亲是一个女孩时,黛比的母亲曾自己游过英吉利海峡.
我有俩个问题：
1.这里的when she was a girl为什么指的是黛比的母亲?怎么看出来的.
2.这句话怎么写：他们当中还会有戴比的母亲,当黛比是一个女孩时,黛比的妈妈曾自己游过英吉利海峡.

1.这是一个长结构的从句,句中的逗号省略不看,这里的who swam the Channel herself 是修饰的Debbie's mother.Debbie's mother who swam the Channel herself 是指那个曾经在英吉利海峡独自游泳的人就是戴比的母亲.而when she was a girl则是作为时间状语来修饰前面那个从句的swam,指游泳的时间,she was a girl就是一个表示时间的状语.现在再来看那个逗号,后半句则都作为修饰语来修饰句子中心语Debbie's mother,所以那个girl就指的是黛比的母亲.

2.Among them will be Debbie's mother,she swam the Channel herself when Debbie was a girl.