«Gnome Invasion» by Eileen Cook

The third in a series of books about Willow's adventures as she masters her secret fairy powers, navigates sprite training, tries to ignore her perfect older sister, and maintains a friendship with Katie, the most un-normal of humans. Willow Avery seems to be advancing in her fairy training with alarming speed. In addition to being able to talk to animals (a very unusual power), she can also fly! But it isn't all good news. Willow's human bff, Katie, has discovered that fairies exist and that's put the Averys in a difficult position. They're under review from the Fairy Council as to what humans' knowledge of fairies could mean. Meanwhile, Willow is entering the school science fair and she's vowed not to use her magic to help her win. So she tests different methods of watering plants the old fashioned way: trial and error. However, a vindictive garden gnome, Jakob DeGroot, is appalled at her plant abuse and does everything in his power to thwart her science project. Of course, drama continues with Bethany and Katie, and new crush Nathan at school. And it looks like Jakob might be meddling with her human classmates' projects too! Can Willow stop the meddling gnome and still be able to compete–all without magic?