Ever since my friends brother died she has been having lights flicker in every room she goes into?

My friends little brother died last year, he was 16 when he died. He was disabled. He was born normal up until he was 4, he started falling over all the time and ended up being diagnosed with something( i don't know what it was called). He slowly turned into a vegetable, it got to the point where he couldn't even move any part of his body, he could only blink, and he had to be fed through his belly button with a tube. Anyway, he died last year as I said. I was at my friends house today and I was in her room(which was his room when he was alive) when I seen the water in my water bottle start shaking, and I said "wtf?" my friend said "what"? and I said "didn't you see the water moving on it's own, wtf"? and she said "oh, that was probably Dion" (Dion is her brother who died). She told me after that lights flicker all the time when she is alone in no matter what room she goes into, ever since Dion died, she was in my room later because we came to my house and I went into the shower, when I came out she told me the light was going crazy flickering, and I could tell she was not lying. Do you think it is her brother? Why is he following her, why is he still here? Also their cat has changed so much since Dion died.