Tides of Magic. Charley Deacon, #1

Meet Charley Deacon. She's failing out of uni, being near the sea makes her inexplicably ill, and now her sister has gone missing in suspicious circumstances. Her only hope of finding her may lie with an impossibly old woman who lives - you've guessed it - by the sea. Welcome to Inver Aora, a tiny settlement on the coast of New Zealand's South Island. It has a holiday park, a woman who may or may not be a witch, and not a lot else.
Most people can't find their way here, but the locals find it hard to leave. If there's anything weird going on, they're not in the habit of talking about it. Charley might be the least likely person to show up in Inver Aora, but it also might just be the place she discovers new powers, her own purpose, and some people that make her want to stick around.