英语中，完成时态里非延续性动词可以用在从句里吗？

可以
但楼上的是延续性动词
The pen she has bought is there.
这句就可以了

当然可以了，如别人给你的例句。你可能没表达清你的意思吧？

当然可以.
eg:He said that he hadn't finished his homework before his mother came back.

可以。
She says that she has been here for 2 years.