She is the feminine third-person, singular personal pronoun (subjective case) in Modern English. In 1999, the American Dialect Society chose she as the word of the past millennium.[1]
When by convention feminine gender is attributed to things (e.g., a ship, a carriage, a cannon or gun, a tool or utensil), she is used instead of it to denote it.
When natural realities (the moon, planets named after goddesses, rivers, the sea, hurricanes, the soul) and social realities (a city, a country, an army, the Church, and others) are personified as feminine, she denotes them as well.
She is also used attributively with female animals, as in she-ass, -ape, -bear, -dragon, -wolf, -lion. In early modern English she was occasionally prefixed to masculine nouns in place of the (later frequent) feminine suffix -ess.
Sometimes she is prefixed to nouns to attribute feminine character to or emphasize or intensify the feminine attributes of a thing:
Instead of her, she has been used as an object or after a preposition both in literary use (now rare) or vulgarly as an emphatic oblique (object) case.
The use of she for I (also for you and he) is common in literary representations of Highland English.
She is probably an alteration of the Old English feminine form of the demonstrative pronoun seo ("that one").[2]
Although she was a lexical alteration of an Old English pronoun, its grammatical place in Middle English was not determined by its lexical predecessor's grammatical place in Old English. According to Dennis Baron's Grammar and Gender:
In 1789, William H. Marshall records the existence of a dialectal English epicene pronoun, singular "ou": "'Ou will' expresses either he will, she will, or it will." Marshall traces "ou" to Middle English epicene "a", used by the 14th century English writer John of Trevisa, and both the OED and Wright's English Dialect Dictionary confirm the use of "a" for he, she, it, they, and even I. This "a" is a reduced form of the Anglo-Saxon he = "he" and heo = "she". By the 12th and 13th centuries, these had often weakened to a point where, according to the OED, they were "almost or wholly indistinguishable in pronunciation." The modern feminine pronoun she, which first appears in the mid twelfth century, seems to have been drafted at least partly to reduce the increasing ambiguity of the pronoun system…[3]
Thus in Middle English the new feminine pronoun she established itself to satisfy a linguistic need.