In the quote "A pardon is valid whether accepted or not". So yes, you can pardon someone who doesn't need it/want it.
If a person who is under investigation claims they did nothing wrong. And they claim they are totally innocent. If that person is pardoned even if they do not want it, then that person has been cheated out of being proven innocent. If I am innocent, I want to be able to prove it.
So far Hillary has not indicated in any way that I know of that she is in need of being pardoned for anything.
At least Nixon resigned, which was a sort of admission of guilt. Hillary laughs at the thought of being investigated. She says repeatedly, 'Let them investigate. I did nothing wrong.'