The Tombs of Atuan is a book about captivity and naming and the nature of identity. It is technically a children's fantasy novel. Le Guin was writing something serious.

Tenar has been given a name that isn't hers — she's been called The One Whom Is Eaten since childhood, a ritual name that makes her property of a dead god — and she has accepted it so completely she doesn't know she has. Ged gives her name back, and that scene is one of the more quietly devastating things I've encountered in any fiction.

What Le Guin understands is that identity is maintained by others as much as by oneself. The Priestesses maintain Tenar's erasure not through active cruelty but through the ordinary operations of a system she was raised inside. The horror is structural, not melodramatic. That's a more sophisticated analysis of how power works than most books written for adults manage.