Looks like everyone who had anything to do with the old man she married for the money ended up dying. First the old man died, then the old man's son died, then Anna's son died, then Anna died...
The money is cursed.
Howard Marshall lost a wife before he even met Anna - IIRC, her name was Betty.
And then his mistress (the unforgettably-named Lady Walker) died on the operating table.
Everyone who's ever touched J. Howard's money is dead.