Evil adopted girl book

I’ve been trying to identify a book I read in the late ’90s for YEARS. It was an adult horror novel about a young adopted girl (maybe 9–12) who was creepy/evil from the start. She killed animals, had an unsettling crush/obsession with her adoptive father, and I think she tried to push her adoptive brother into a lake.

I remember there being a horror/supernatural element too. I bought it at a used bookstore, so it could have been published much earlier.

After a ton of research I thought it could’ve been The Godsend but she wasn’t a baby when she was adopted, she was older. PLEASE tell me this sounds familiar! Thank you for any help!