Heart of a Dolphin by Catherine Hapka

Sometimes you find a friend where you least expect it...When Annie spots a dolphin trapped in fishing line in the cove near her house, she rushes to free him. Everyone cheers when she returns to shore, but only Annie knows that she and the dolphin have forged a special bond. He's become her friend -- and keeps returning to the cove to visit and play!Meanwhile, out of the water, nothing is going right. Annie's best friend, Emma, has changed, and keeps ditching her to hang out with snobby Morgan. At home, Annie's busy parents barely seem to have time for her, and she's stuck with her hyper younger brother always tagging along. Then a misunderstanding with Morgan makes things even worse... and ultimately leaves Annie alone and in danger. Can her dolphin friend help her when she needs it most?