The girl who she said that she is a pirncess这句话有没有语法错误,若有的话,

错啦,首先,Who后面是定语从句,who是引导词,在从句中是充当主语的成分的,所以从句中的she就是画蛇添足了,正确的应该是：
who said that she is a pirncess
另外,这不是一个句子,只是一个名词性结构,可以在句子里充当主语、宾语或表语
最后,时态问题,前面是that she is a pirncess是间接引语,要跟said的时态一致,不能用is,而是was
The girl who said that she was a princess will come here tomorrow.