she is a subject

This is wrong sentence. He/She is use for human being . But "subject" is not human being it is non living things. So you can't write "she" for this . You can write this sentence like that :- It is a subject. We also put "it" for the animals. Example :- The dog is licking its legs.

Yes, "she" is a subject. Examples :- She is a good girl. She goes to school everyday.

yes