She is a girl we were talking about这句话有无语法错误？

没有错
但是如果 the girl we were talking about 更合适

a 翻译 她是我们刚才谈到的其中一个女孩
说明哟很多女孩

the 翻译 她是我们刚才谈论的女孩
只有一个女孩

定语从句没错
但是a改为the 更好

we are talking about She is a girl `

She is the girl we are talking about