I think it does exactly the opposite as far as testifying goes. If she holds a pardon then she can't plead the 5th, since it's impossible for her to incriminate herself then.
Good point... Maybe. But she certainly could, the Clinton's have bemoaned the "they're out to get me" forever, so would income the 5th no matter what, I'm certain. Or she could do as she has done more than once in the past, use the "I don't recall" exemption. Lol...