The ghost in the swing

It's a young preteen's murder mystery. "Underneath the hollyhocks, where a head received some knocks, lies a answer/treasure/message in a box" was a message the young girl ghost named Felicia gave to the visiting girl. A young girl is sent to spend the summer with her great-aunt in the country (Maine, New Hampshire?) that she has either never met, or doesn't remember. She's bored and doesn't want to spend the summer there. Her great-aunt wears roses and peppermint perfume that the young girl likes. The house is old with old family pictures around and not much to do. She begins to explore the surrounding property where there are apple orchards and gardens. There's an old gardener who I recall is either related or is just an old family employee. One night she hears a young girl singing on a swing in the orchard. The young girl discovers after some time it's a ghost. The ghost's name is Felicia, who tells the young girl that she died when she was young. She sees the picture of Felicia on the wall of her aunt's house and asks questions about her. Turns out Felicia was a bit of a tomboy who was the aunt of the great-aunt and suddenly disappeared when she was 12. The young girl solves the mystery of Felicia's disappearance after Felicia gives her bits of clues in sing-song. The young girl goes home with her family at the end of the summer after realizing she had a wonderful time.