Looking for YA sci-fi from the late 80s regarding a telepathic society

Question

I'm looking for a book I read in the late 80s about a society that communicated only through telepathy. The main character was a female in her teens. In the beginning her mom had a baby and 'reached out' to it telepathically, baby could not respond so it was killed. The girl was an outcast because she kept a wall up preventing others from communicating with her. She met a humanoid 'alien' whose craft had crashed and he was instrumental in her seeing the truth of the tests her society put forth for their teens' rights of passage. Any ideas would be appreciated!

Answer 1

This may be Pamela Sargent's Watchstar (published 1980), as suggested in the unaccepted answer to a recent (and very similar) question, and which was accepted as an answer to this older but less detailed question.

Per the summary on Goodreads:

Alone in the desert, Daiya is faced with 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.

As elaborated on by goodreads.com user Nicole in her review:

The society that has evolved is telepathic and telekinetic, agrarian and insular, with low population density. Adults communicate with each other exclusively by telepathy, can heal themselves with their psychic powers, can fly and lift objects and much more. However, all of this is treated in the book the same way walking or using a tool would be treated - it's just the way life is. There is no written language; knowledge is passed on through the Net, the psychic collective that everyone is a part of. People live in nuclear family units with many children, the children move out and start their own families, and once the parents become empty nesters, they enter the next phase of their evolution. Their selves begin to merge with this collective consciousness until they become completely one with everyone...

Some infants are born without this psychic ability; they're called solitaries. The solitaries are considered non-people and are euthanized shortly after their birth. For them to live would destroy the harmony of the village, say the elders. Objections to this or anything else rarely come up - to object to tradition, or to have a different idea, or to be alone, is to destroy what is harmonious about society...

Daiya goes into the desert to prepare for her ordeal, unnerved by the comet that has been hanging in the sky. She sees something odd, and investigates. She finds a young man who has come down from the sky in a shuttle to investigate her world. He lives on the comet, his people originally came from Earth, and their post-singularity evolution has been very different. And - oh yeah - he's a solitary.