There are NO dogs killed in this movie. Not sure what the other person is talking about but they must have the wrong movie. NO DOGS or any animals are killed in this movie!
Yes a sister’s past addiction is brought up into question when she goes missing. It’s also shown when Annie goes to visit a highschool friend and the house that she lives in is full of other people on drugs.
Annie is traumatized from her childhood as well as the aftermath of the movie. While she doesn’t have flashbacks she does have frequent nightmares and crying sessions.