A Girl Called Blue

Blue O'Malley, a young orphan, was left outside the orphanage at Larch Hill by her mother when she was just a baby.  As she grew older she as always getting into trouble with the nuns and when she thinks life can't get any worse, her best friend drowns and is never found again.  Blue never thought she would find happiness until she found a sixty year old woman and her thirty year old son, the Mooney family.

I think the character that changed in the book was Sister Regina.  At the start of the book she was a bully to the children, she would hit them for no apparent reason and punish them for the smallest of things.  She would also mutter hurtful words under her breath, knowing that the children would hear it, such as orphan.
By the end of the book she realized that what she was doing was wrong, thanks to a brave young girl who finally confronted her.  After this incident, she decided she needed to be more like a mother than a bully to the children and so started complimenting them and let them have some fun.