"What Katy Did Next" by Susan Coolidge

The third Katy book just might be my favorite.  Seeing Katy being as kind and intelligent and capable as ever, but now more mature and less prone to get into scrapes -- that was absolutely a delight.
Now about twenty, Katy Carr helps out a family friend by taking care if her daughter for several weeks.  The daughter becomes very fond of Katy, so when the mother decides to go to Europe for a year, she asks Katy to come along.  Not as a nanny for the daughter, but only as a friend.
Katy has a series...