Lynne Jonell - Emmy Series (Books #1-3)

#1. Emmy and the Incredible Shrinking Rat:
Emmy was a good girl. At least, she tried very hard to be good. She did her homework without being told. She ate all her vegetables, even the slimy ones. And she never talked back to her nanny, Miss Barmy, although it was almost impossible to keep quiet, some days. She really was a little too good. Which is why she liked to sit by the Rat. The Rat was not good at all .

#2. Emmy and the Home For Troubled Girls:
Emmy Addison was an ordinary girl - almost. If you didn't count the fact that her parents were rich (very), her best friend was a boy (and a soccer star), and she could talk to rodents (and they talked back), she was very ordinary indeed. But she hadn't been that way for long . . . It was only a few weeks ago that Emmy and her friends Ratty and Joe got rid of the evil Miss Barmy, the nanny who had nearly ruined Emmy's life - and the lives of five other girls who went missing. Miss Barmy is now a rat. How much harm can she still do?

#3. Emmy and the Rats in the Belfry:
Emmy was not an ordinary girl. She could talk to rodents. She could shrink to the size of a rodent. And just a few weeks ago, she had even become a rodent to defeat her evil former nanny, Miss Barmy.
Emmy's parents, unaware of their daughter's other life, ship her off to visit two elderly aunts in Schenectady. Emmy figures her life will be ordinary at last, if rather boring. But she didn't count on her friend Ratty, whose search for his long-lost Ratmom brings him more than he bargained for.