"She" is used to refer to a female person or subject that has been previously mentioned or is easily identified in context.
She vs. He
As you might've known already, 'he' and 'she' are the only gender-specific personal pronouns in the English language. Here, we'll explain them in more detail.
'It', 'she', and 'he' are personal pronouns that show person and number. 'He' and 'she' also show gender. Read this article to know these three pronouns.