Etymology
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her (objective case)
Old English hire "her," third person singular feminine dative pronoun, which replaced accusative hie beginning in 10c. See he. Cognate with Old Frisian hiri, Middle Dutch hore, Dutch haar, Old High German iru, German ihr.
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her (possessive case)
Old English hire, third person singular feminine genitive form of heo "she" (see she). With absolute form hers.
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hern (pron.)
"hers" (dialectal), from her + adjectival -n.
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hir (pron.)
Middle English obsolete form of her.
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yourn (pron.)
dialectal possessive pronoun from your, attested from late 14c. See her.
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herself (pron.)
emphatic or reflexive form of third person feminine pronoun, Old English hire self; see her (objective case) + self. Originally dative, but since 14c. often treated as genitive, hence her own sweet self, etc. Also compare himself.
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hers 
c. 1300, hires, from her; thus a double possessive. Possessive pronouns in Modern English consist of the predicative (mine, thine, his, ours, yours, theirs) that come after the subject, and the attributive (my, thy, his, her, our, your, their) that come before it. In Old English and early Middle English, they were identical. To keep speech fluid, speakers began to affix an -n to the end of predicative my and thy before words that began with vowels. This began late 13c. in the north of England, and by 1500 was standard.

Then the predicative and attributive pronouns split, and the remaining pronouns in that class took up -s, the regular affix of possession. But the non-standard speech of the Midlands and south of England extended -n throughout (hisn, hern, yourn), a habit attested from 14c. and more regular than the standard speech, which mixes -s and -n.
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*ko- 

Proto-Indo-European root, the stem of demonstrative pronoun meaning "this."

It forms all or part of: cis-; et cetera; harass; he; hence; her; here; him; his; hither; it.

It is the hypothetical source of/evidence for its existence is provided by:  Greek ekeinos "that person;" Latin cis "on this side," citra (adv.) "on this side;" Old Church Slavonic si, Lithuanian is, Hittite ki "this;" Old English hider, Gothic hidre "hither."

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his (pron.)
Old English his (genitive of he), from Proto-Germanic *hisa (source also of Gothic is, Old Saxon is, German es). Originally also the neuter possessive pronoun, but in English it was replaced in that sense c. 1600 by its. In Middle English, hisis was tried for the absolute pronoun (compare her/hers), but it failed to stick. For dialectal his'n, see her.

In 16c.-17c. commonly used in place of a genitive inflection after nouns whose nominative ends in -s (for example, "When this Book became a particular book, that is, when Moses his book was divided into five parts, I cannot trace." [Donne, "Essayes in Divinity," "Exodus," 1651]). Here it is perhaps an expanded vocalized form of 's, originally -es. This tendency began in late Old English and was obsolete from c. 1750.
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she (pron.)

"the female person referred to," third person nominative fem. pronoun, used as a substitute for the name of a female or anything regarded as female, mid-12c., probably evolving from Old English seo, sio (accusative sie), fem. of the demonstrative pronoun (masc. se) "the," from PIE root *so- "this, that" (see the).

The Old English word for "she" was heo, hio, however by 13c. the pronunciation of this had converged by phonetic evolution with he "he," which apparently led to the fem. demonstrative pronoun being used in place of the pronoun (compare similar development in Dutch zij, German sie, Greek he, etc.).

The original h- survives in her. A relic of the Old English pronoun is in Manchester-area dialectal oo "she." As a noun meaning "a female human being, a woman," she is attested from early 14c. Also used to signify "female" with the names of other creatures (late 14c.; she-wolf, etc.). The attempted gender-neutral pronoun form s/he is attested by 1977.

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