I don't think Melissa believes in ghosts. I believed in ghosts for a very long time but it turned out (specifically in my case) to be OCD. Melissa doesn't believe in ghosts because it's funnier that way. Ellie believes in ghosts because y'know what when you dream the future all bets are kinda off on the whole supernatural thing.

Do you see the chandelier on the table? It is Chekov's Chandelier. It will come back later.