Clammed Up by Barbara Ross
In Clammed Up, Julia Snowden, our amateur sleuth, has a legitimate reason to investigate the crime. Her family's business, the Snowden Family Clambake, was already having financial difficulties, but finding the dead body on the island has shut them down, and each day of business missed is one day closer to the bank calling their loan. Oh, and the guy she has a crush on seems to be one of the main suspects.
Julia and her family are easy to like. They stick together, even when they fight. The small town feel was well-done too. The locals all know each other and know how much the tourist season means to the town. Old friends are loyal, but know each other's backgrounds too.
I also loved the Maine setting. It's nice to visit other places while we're all stuck at home. I went to Maine with my family once when I was younger. Pretty much all I remember was cold and gray, so...