Klara and the Sun by Kazuo Ishiguro

Klara is an Artificial Friend who longs to be picked by a young girl.  She resides in a store where the manager tells her how to do her best to represent the store and other artificial friends.  She receives nourishment from the sun (she is solar powered) and while in a storefront window, watches a homeless man sit each day with his dog across the street.  One day, neither the homeless man nor his dog rise and Klara is afraid they are dead.  But when the sun comes out the next day, they  rise and seem to be better than before.  A machine is parked in front of the store that produces terrible pollution.  When  it is moved, Klara sees the homeless man become reunited with a woman as they embrace.

When Klara is picked, the girl who asked for her, Josie, is a 'lifted' youngster (genetically edited) who has trouble with her health.  From Josie's room, Klara observes the sun sets, goes to rest, on the far side of the field in a barn.  Josie has a  friend, Rick, who is not lifted, but is brilliant with drones.  They play and squabble.  But Josie's health gets worse.  Klara comes up with a plan to ask the sun to heal Josie with his special restorative nutrition.  So she travels to the barn with Rick's help.  She offers to destroy the pollution machine in exchange for Josie's improved health. 

The family, including Klara go into the city for Josie's 'portrait' where Klara discovers it is a replacement artificial friend body that upon Josie's death is to become a new body for Klara.  Klara is convinced that her bargain with the sun will result in a healthy Josie.  She finds the pollution machine and with the help of Josie's father, takes some of her own lubricant and pours it into the exhaust of the machine, disabling it.  Now Klara plans to watch the sun restore Josie.  But Josie does not get better.

While the family surround Josie, expecting her to die at any moment, odd weather comes through the area where the family lives.  Klara suddenly gets everyone to go into Josie's room and she open's the blinds so that the sun floods the room.  Josie sits up and says she is feeling better.  Klara's sacrifice has not been in vain.

Josie eventually gets well enough to go off to college.

The book ends with the manager finding Klara in a storage yard, discarded, but spending her time reminiscing her time with Josie.