The Tail of Emily Windsnap

I suppose some nostalgic part of me still loves the idea of mermaids, which is why I borrowed this from the library. It's a good book for a middle school-aged child. The story revolves around a young girl who suddenly discovers that she's a mermaid in the water and human on land, although for some reason she's never experienced the transformation in, say, the shower or bath. It encourages sneaking out at night, keeping secrets from adults, assuming your mother is a moron who needs to be cared for, and being suspicious of authority figures, but if you're okay with that, it's a decent story.