She doesn't really have to pretend with Harry, though, if you see how it is. She does menial things like fetch his belongings because it's the bare minimum of what everyone else would expect, and those menial things are also what I think he's comfortable having her do, because he's always had someone around to do them for him, hasn't he?

So she's not that devoted. On the surface, sure, but not deep down. Not like Dennis, say, who didn't have any idea who he was beyond being a mudblood.