第二句多了一个 but ,全句可以是:
No one but her knows Russian.( No one 是主语 )
No one but her herself knows Russian. ( herself 是 her 的同位语)
No one but she herself knows Russian. ( herself 是 she 的同位语)
No one but she knows Russian.
第三句也可以单独用人称代词:
It looks as if no one except him can be there early.
【说明】以下内容引自《牛津英语用法指南》第四版:
在 but 后面,通常用宾格代词(me, him 等)。在较正式的文体中,主格代词(I, he 等)可以用在动词前面。
Nobody but her would do a thing like that. 除了她,没人会干出那种事情。(较正式的说法:Nobody but she ...)