What is the earliest science fictional or fantastical example of a woman being sterilised to take on new power?

I'm sure there has to be an earlier example, but in Terry Pratchett's 1981 novel, Strata, the treatment for immortality also removes your ability to have children. The 1988 novel Cyteen has a similar effect from their rejuvenation treatment. In between the two years, published in 1985, fantastic novel With a Tangled Skein by Piers Anthony has the female character rendered infertile during her time as an incarnation of Fate because her body is frozen in the state at which she gained the title and therefore a pregnancy cannot develop within her.

Interview with the Vampire is a book from 1976. It starts a series called The Vampire Chronicles, in which "vampirization" causes all of a person's bodily processes to cease:

Upon their transformation, the newly born vampire will forever lose all natural bodily fluids (with the exception of blood) and their bodily functions will forever cease. It is because of this that vampires are unable to reproduce through pregnancy (...)

This may be stretching the definition of "sterilize" a bit, but consider the 1967 novel Lord of Light by Roger Zelazny, which takes place in a world where people can change bodies in an imitation of reincarnation. When the god Brahma is murdered, the goddess Kali is chosen to be promoted as the new Brahma; this requires her to switch from her female body (giving up the ability to have children the female way) to a male one.

In Shakespeare's Macbeth (1606), Lady Macbeth calls on evil spirits to "unsex" her, giving her the supernaturally-charged determination to go through with the murder of Duncan:

Come, you spirits
That tend on mortal thoughts, unsex me here
and fill me from the crown to the toe topful
Of direst cruelty. Make thick my blood
Stop up th'accents and passage to remorse,
that no compunctious visitings of nature
Shake my fell purpose, nor keep peace between
Th'effect and it. Come to my woman's breasts
And take my milk for gall, you murdering ministers...

This renunciation of her traditional womanhood is drawn from contemporary beliefs that witches' bodies were tainted by their association with dark powers. That includes the ideas that her blood would not flow properly, that she would have unusual marks on her body, etc.

This is not necessarily fully "fantastical" since it's based in a belief that this sort of thing really happened, but it is a pretty clear antecedent to the other examples presented: Lady Macbeth gives up fertility in order to gain power, in a classic magical-style exchange. The cultural weight of Shakespeare on following writers is also pretty considerable.

If technologically-enforced virginity counts (it's not technically sterility, but it's sufficient to prevent having sex in the first place) then you could consider The Spell Sword (1974) by Marion Zimmer Bradley.

The Keeper of a laran-matrix Tower (a psychic/magi-technical organization) is bound through the laran matrix to virginity, to the point that the laran will strike down anyone who tries to have sex with the Keeper. This is mentioned in The Spell Sword, and fully shown in the sequel The Forbidden Tower.

These "old ways" of binding a Keeper are described by Wikipedia as "neutering" so I think it's close enough to be worth considering as a fit for the question.