Originally a variant of 姐 (jiě, “elder sister”). Later repurposed as a feminine third-person pronoun influenced by European languages, with the glyph being the result of replacing the 人(“person”) radical in 他(tā) with 女(“woman”). Linguist Liu Bannong is credited with coining this use around the 1910s (Bi, 2013).
No major Chinese dialect distinguishes between “he”, “she” and “it” in spoken form, and Mandarin 他／她／它 (tā) is the only instance where such a distinction is made in written form. Thus see the table below for words for “she” in other varieties of Chinese.