So I read this book in 2020 or 2021 and I believe it was written roughly around that time. The author is a woman with a unique name (which for the love of cheese, I cannot recall) and her bio said she lives on an island off the coast of England (could be Channel Islands) or possibly coast of Australia! Oh man, I’ve really forgotten!

The story is written first person from the perspective of a girl as she grows up, and then also as she is an adult. I forget how her father died, but I think he was on a boat at sea and never returned. The girl is sent to live in a house on the coast with a woman guardian, who is not her mom or stepmom, and their relationship is curt. There is a creepy male family friend who drives up every other week or so to check in on them and I think gives them money.
At some point, a German pilot crashes his plane into the ocean, swims to shore, and comes to their house. They help him and hide him in their attic. As I recall, he speaks little English. The little girl develops a loving sweet relationship with him, and he teaches her to draw. The girl’s guardian woman falls for him, and the little girl feels jealous of their relationship.  At some point later in the book, the creepy man is coming over and the girl is upset with her guardian, and intentionally leaves the door to the attic open where the creepy man will hear them talking. The creepy man discovers them and basically tells the man to walk into the ocean, knowing he will not survive the freezing water.
In the meantime, in the present, the now  adult little girl is planning the day she will die and leaving a note for her neighbor letting him know. She is visited by a teen girl who is sitting on her fence (and I think she is the daughter of the creepy man and her guardian). I know it’s complicated!
The grown little girl does end her life as she planned, but it’s not graphic or violent.
I cannot remember any names, but I think the time is WW2 because of the German pilot.
Thank you so much for any ideas! I’ve searched so many searches and authors and come up empty.