Iirc hearsay isn't evidence. She had no proof. She apparently got details wrong eg number of shots, where they were shot, who shot them (she said a hitman).
What her statement seems to have done is lead to other interviews where people unconnected to the family, who had nothing to gain, said JB had mentioned if his family all died at WHF, he'd inherit everything.
Plus she confirmed the window could be opened from the outside - which JB later confirmed he knew and that he'd used it to access the house. She also confirmed the caravan burglary story - which JB then admitted.
So even if you disregard everything JM said. JB confirming that he broke into his family business spoke to his attitude to money and family. JB confirming he had used the bathroom window to access the house, meant the murderer didn't need to be one of the people dead in the house.