Lost & found / Jacqueline Sheehan.

Enhanced descriptions from Syndetics:

An unforgettable tale of love, loss, and moving on--with the help of one not-so-little dog...

After the death of her husband, Rocky flees to Peak's Island, a tiny speck off the coast of Maine, a million miles away from everything she's lost. Taking a job as an Animal Warden, Rocky meets Lloyd, a large Labrador retriever, who enters her world with a primitive arrow sticking out of his shoulder. And so begins a remarkable friendship between a wounded woman and an injured, lovable beast.

Can the magic of Peak's Island and its quirky residents heal Rocky's pain? As the unraveling mystery of Lloyd's accident and missing owner leads Rocky to an archery instructor who draws her in even as she finds every reason to mistrust him, she discovers the life-altering revelation that grief can be transformed...and joy does exist in unexpected places.