In The Mermaid's Mirror (Houghton Mifflin, 2009) by L.K. Madigan, Lena has spent her whole life near the ocean, but isn't allowed to surf like her friends because her dad had a surfing accident years ago, but now that she's almost 16 she wants to learn. Dad and her stepmom are adamant about her not learning. Which, of course, doesn't make sense. When she sees a mermaid, Lena has to learn, and only then will she find out why she's to stay out of the ocean.
Author L.K. Madigan lost her battle with cancer earlier this year. Her husband has periodically posted to her blog since her death in February.