I'm not sure what you mean by "old". Two movies with drowned sisters come to mind. Neither one has a body kept in a casket though the first has a shrine at the bottom of the lake. In both of these, the brother blames himself for the accident.
Oh my god! I have been trying to find this for years. I remember a brother and sister playing outside as small children near a small river near their house when the sister loses her footing and slips and hits her head on a rock, falls in and drowns. The only other thing I remember is her body in a casket in a room at the top of the stairs and when her brother goes up there the casket is open and she is laying there and suddenly looks at him. So freaky! What movie is this!!!