I don't expect everyone to understand all the rules of grammar since it's not even taught anymore, but I cannot believe this is an issue. Were you never taught this in Elementary school, or by your parents? "This is she" is antiquated but DEFINITELY correct. I promise you. May I be stricken dead this instant if I am wrong.

And that first comment was not meant to insult educators. I'm an English teacher, and I can tell you, the curriculum does not focus on grammar. None of my students have ever diagrammed a sentence.