Or maybe we are just concerned about our knowledge and the possibility that some people are taught wrong about the english grammar which is used all the time and the fact that english grammar exams exist Ed22SAS you can't be sure about other people's intentions when they're not directly said and your post doesn't help anyone and therefore useless. I'm not sure why you're here when you don't intend to learn from these arguments that you read.

I thought I, She, He, We, They are used as subjects and Her, Him, Her, Them, Us are used as objects (not sure if object is the term)
ex: It's me. - in this sentence the subject is It and the sentence is saying that It is Me or in another case like in the sentence This is a pen, This is equal to It and pen is equal to me.
Correct sentences for me:
She and I are going out. (subject:She and I object:going out)
It is between her and me. (subject:It object:her and me)
I am her. (subject:I object:her)

Her can be used in more than one way right? Not just for possession. Why don't other people know that?! Isn't that weird? Her can be an object too aside from using it for possession (her ball, her hand, etc.). Ex: I told her. (subject:I object:her)

And you can't just interchange the subject and object in the sentence. Ex: "It is me." cannot be "Me is it." To make the sentence this way, it will be "I am it." So you can't use that "interchange" thing as a basis for making a rule like "She is me." is wrong because "Me is she." is wrong, because we all know that the first sentence is right and the 2nd is wrong.
"This is her." is not wrong. I've read a post saying that it is wrong because when you interchange the nouns, it will be "Her is this."! What?! When you interchange the nouns in "This is her.", it will be "She is this." (meaning: she is this person right here) "She" is used as a subject and when it becomes an object, it becomes "Her". Get it?

You are smarter than I is different from You are smarter than I am and it's not a short version. If you're going to use the first sentence, it should be You are smarter than me. In You are smarter than I am, "I am" refers to how smart the person referred to is. It is not the same as the "I am" in the sentence "I am a person". which is the subject in this case and not the object.

I've heard characters in tv and movies use "This is she." for me, this is not grammatically correct because there is no rule that can say that it is correct. Maybe some people are just used to saying it or heard it from supposedly smart people and trusted them right away. It's not wrong to use it as long as other people understand, but, you shouldn't use it in arguments like this.