是Whom.
Who & whom 的应用别说咱们,即使是说英语的老外们有时也会困惑.
我的理解是这样的：-
看到一个句子的时候,代入一个代词,看究竟是主格还是宾格最适合.
主格的话,用who
宾格的话,用whom
打个比方说,这个句子：Jonas is the man ______ I went fishing with last summer.
I went fishing with him last summer 还是 I went fishing with he last summer 正确呢?
当然是前者,I went fishing with HIM last summer,是宾格,因此应该用whom.
另一个句子,Emily is the girl ______ did the job.
She did the job 还是 her did the job正确呢?
当然是"she did the job"正确,是主格,因此这个句子应该是 "Emily is the girl WHO did the job".
绕回楼主的问题,
在假设代词句中代词是"她”的情形下,楼主觉得应该是 "he is speaking to HER“ 还是 "he is speaking to SHE"呢?当然是"he is speaking to HER",是宾格,因此就用"whom".:)