核心问题
I don't think she knows French, does she? 这里的反意疑问句为什么是 does she，而不是 do I?
词典解答
可否定转移的动词的否定常常转移到宾语从句中去：
I don't think she knows French. I think she doesn't know French.
而反意疑问句是针对被转移否定的从句而说的,所以当然要 does she? 而不能 do I? 类例:
- I didn't think he was happy, was he? 我认为他并不幸福,是不是?