Not all connections with other people have to be deep or lasting, but she too easily writes off those three as not worth her time
She's giving them her time. What she's not doing is forming a sense of attachment to them.
Neither Adachi nor Shimamura form attachments as readily as do other people. Shimamura is much better than Adachi at ordinary social behavior, in part because Shimamura has much better parents.
But neither has a responsibility to attach to those around them. And Shimamura is not so much as hurting the feelings of the three girls who want to be her friends. She's pleasant to them, they see her as a friend, and she's not scheming to subvert their interests. Nor does she think that they ought particularly to care about her.
However, in the novel, to which this manga conforms fairly well, neither girl is on the autism spectrum. Their innate capacities to understand other people are quite superior.
Adachi wasn't moved to exercise her ability until she met Shimamura, so she's in unfamiliar territory, but she builds most of many years worth of a map in just three years.
If we accepted Bettelheim's once popular theory of “refrigerator mothers”, then indeed we'd see Adachi as an autistic who is later largely cured. But the present understanding of autism is quite different (and Bettelheim has been exposed as a cruel charlatan).
Cured? Cured??? Autism spectrum disorder isn't something that can be "cured" in any sense of the word.
