"This is she" and "she is this" actually don't mean the same thing, therefore they are not interchangeable, and this simple fact shuts down the second source's argument. In "this is her" you are talking about "this" and in "she is this" you are talking about "she". I don't know any better way to explain this other than this coming up example, so bare with me. If I have the power that makes anything I say come true, saying "this is her" would cause "this" to transform into "her", this would become her, but if I say, "she is this", "she" would become "this".