Young adult book about a girl whose parents pass away.

Around 2016/2017 I read a book about a girl whose parents pass away and she has to go live with her uncle that lives alone on a little island in the middle of a giant lake. The uncle is a bit creepy and so is the house.

I remember she’s fascinated with these flowers that are in a green house that were purple if I remember correctly and towards the end of the book she tries to leave the island and I think she had a companion with her but it wasn’t human.

I remember it to be such a great book and i have tried for months and checked every book in my house and I can’t find the name for the life of me.