Every girl is a Kumari.

It is said that Newar women undergo three marriages in their lifetimes. The first, known as Ihi, takes place between the ages of five and nine; the girl marries a bel fruit, which symbolizes the god Shiva. The second, called Bara Tayagu, occurs just before the onset of menstruation; the girl spends twelve days in a room shielded from sunlight, and on the twelfth day, she worships the sun, thereby marrying the sun god Surya. The third marriage is to a human male—a life partner.
While marrying eternal, immortal deities like Shiva and the sun god serves to ensure that a woman never becomes a widow, the fact that both of these initial ceremonies take place before the onset of menstruation is also significant.
In Tantra (Esoteric Buddhism/Hinduism), women are viewed as embodiments of Shakti—the primordial cosmic force that empowers male deities—and this force is believed to reside in its purest form within the bodies of pre-pubescent girls. Consequently, goddesses such as Durga, Kali, and Taleju are said to inhabit the bodies of Kumaris (living goddesses). This concept extends to ordinary Newar girls as well; on Maha Navami—the ninth day of Dashain, the most important Hindu festival, which commemorates the goddess Durga’s victory over the demon king Mahishasura—families perform rituals to worship these girls, who are believed to harbor sacred power, as Kumaris.
Among the Newar people, young girls are seen as beings who readily host the goddess in her purest form; they serve as bridges between the divine and the human, vessels for the deity, and embodiments of Shakti, the source of cosmic power. This concept is manifested in the figure of the Kumari, to whom the people offer their prayers.
While tradition dictates that the girl selected as the official Kumari must come from specific castes—such as the Shakya, Bajracharya, or Jyapu—it can be said that every young girl is, in essence, a vessel for the goddess and a Kumari in her own right.