Girl 11-14 who has ESP (as does her clan), has to do something or loses it and dies, meets boy (older) from moon or sky city who has no powers, but lots of technology that does same thing. They hook up (which I thought was odd for that age), and their two civilizations meet or something like that. 60-70’s I think. Telepathy was part of it.
That sounds a whole lot like one of Zenna Henderson’s People stories. The People are aliens who look human but who have ESP and other psionic powers. The stories were pitched to a YA audience. They often had girls as protagonists. They were published in science fiction magazines, so having the protagonist meet someone from a high-tech civilization would work.
The People stories were gathered together in two volumes, Pilgrimage and No Different Flesh, and are now gathered into one, Ingathering.
Could this be Watchstar by Pamela Sargent? It was published in 1980.
“Alone in the desert, Daiya is faced with a dilemma that will determine her fate. If she can successfully resolve it she will join the Net of her village, but if she fails, her life will be spent with the feared Merged Ones. Confused and torn between worlds near and far, Daiya harbors a secret of her people, and must find a way to move beyond her discoveries to a safe place where she can survive.”
A long shot. The Chrysalids by John Wyndham?
YOU FOUND IT! — Watchstar by Pamela Sargent (and it turns out a couple of sequels!)