The Moorchild, by Eloise McGraw

Moql loves her life among the Folk- the festivals, the daily routines, and the fun.  But at a crucial moment, she finds that she cannot hide herself from humans as her peers can.  It comes to light that her father was human, and because she is neither one race nor the other, she is a threat to the entire Band because she risks exposing them.

The Prince of the Folk has little sympathy for her.  She is led away from her home and switched with a human baby, and left on her own.  Helpless in her newborn body, she rages and screams and cannot be consoled, except with honey.  In time she grows in size and skill, but eventually forgets all about the Folk and her true origins.

The people of the town, however, have their suspicions.  Saaski, as she is now known, is unusual.  Her skin is dark, her eyes are slanted, her feet are long, and she has a number of unusual behaviors.  She runs up walls and perches in rafters.  And she spends hours roaming the moors alone, a place most of the townspeople avoid.  Eventually sicknesses and accidents begin to plague the town, and the villagers suspect Saaski as the source.  Where will she go if she cannot remain with her family, and the Folk also do not want her?

A really interesting take on the changeling myth from the perspective of the changeling itself.