"This is she" is correct. You can skip all the jargon if you want to. Here's how I remember it: add a silent "who ..." after the sentence. "She who is speaking."

The reason is, you're announcing a subject ("she") who is going to be an actor in the sentence (be followed by a verb). "It is I who come." Not "It is me who comes." "Me" can't do anything, because it's an object. Only "I" can do things like come, speak, etc.

That's also why, you also use the pronoun-as-subject in certain comparisons. "He's better at cooking than I." Not "me." Because it's shorthand for, "He's better at cooking than I am." Not "me am."

Another example: "I like cheese better than she." You're comparing the verb ("like"), not the people ("I" and "she"). You're comparing how much you like cheese to how much she likes it. You're not comparing how much you like cheese to how much you like your friend. "I like cheese better than her," means - this is the literal meaning of this construction - that if you had to choose between the cheese and your friend, you'd pick the cheese.

None of this is a matter of opinion. It's just the way these parts of speech work. Sure, you can misuse them colloquially and still be understood, and if you do use them correctly you might even risk sounding like a nerd for your trouble. Still I think it's important to understand these words for what they are.

I mean, sure, you can use a flathead screwdriver to pry a nail out of the wall - it does work - but that's not what the tool is for, and if you want to use it skillfully it's important to know what it's for and why.