She named Macdonald as the killer.
Not quite. JM told three very different stories.
First, JM behaved as though Sheila was the killer. JM was then clearly delighted to be Jeremy's girlfriend, going on holiday, out for meals and out drinking with him, with no qualms whatosever.
Only after she was jilted by Jeremy did JM name McDonald as the killer, claiming that he was Jeremy's hitman.
Later, when that proved to be untrue because Mathew McDonald had a water tight alibi, JM changed her mind yet again.
JM then told the Daily Mirror, "I sincerely believe" that Jeremy killed his family. JM said much the same to the News of the World", who paid her £25,000 for her story - once the police had given her immunity from prosecution.