The usual case in my world isn't shapeshifter so much as 'just actually physically looks like you and thus can impersonate you.' Except apparently Silas, but that's a 'getting in your head and making you see things' issue. But I don't really know of doppelgängers gone good, which is partly because they all seem to be tied up in something magic. And when you're part of the whole 'die to make something happen' scenario, it doesn't go well for you.
I know what the fans think, so it was refreshing to know that she, at least, isn't so much of an idiot who forgets the important things. What do you think about the fact your actor is married to Willow's actor?