Movie about a girl who befriends a monster (?)

I’ve been trying to find this movie for years and I still can’t remember what it was called, it was about this girl who lived with her aunt by the seaside. I don’t remember a whole lot about it but I remember that the girl wore a yellow jacket, she befriends a monster (I think?) and she owned this little book which had some relevance to the story. I watched it around 2016-2017 on Netflix in the UK