I think the main premise of this book was really interesting and I loved the deep sea setting. I think there was potential for some really complex discussions around personality disorders that was missed though, with the main character Lily having ‘emotional problems’ and often lashing out uncontrollably to the point we’re it’s significantly effecting her and everyone around her, but then brushed under the rug as soon as the situation becomes dire. Speaking of a dire situation, I think the stakes could have been emphasised just a little more, as I always got the impression the characters would get out of their dilemmas, so wasn’t that on the edge of my seat. Also, Harry Potter reference in a book coming out in 2023? Bad look. 
Essentially this has a lot of promise and if you’re a fan of YA looking to get into more deep sea stuff I’d recommend (just why why why is there an hp reference I don’t understand)