Well, it could be a rival seeking power or someone with a personal vendetta against the empress. There are several possible suspects, and the author might keep us guessing until the end.
Well, it's hard to say for sure. It could be a rival manga enthusiast who wanted to have it for themselves or a thief looking to make a profit by selling it on the black market. There are so many possibilities!
According to the search results provided, it was impossible to determine if the empress dowager knew about Fan Xian stealing the key. Although some documents mentioned that the Qing Emperor might know Fan Xian's identity, there was no clear information on whether the empress dowager knew the exact circumstances of Fan Xian stealing the key. Thus, it was impossible to determine if the empress dowager knew Fan Xian had stolen the key.