Don't know Steve but then I don't know if I believe Julie that much even if JB is guilty, I think she was looking after number one when she went to the police rather than thinking of the people who lost their lives.
What did she say that you don't believe? The only lies she would have a reason to tell would be if she
had conspired with him to commit the murders or conspired to help obstruct justice and in such case the lies would be to conceal her guilt. So the lies would be failing to tell her full role. It would mean Jeremy told her even more and she agreed to assist him. While that would be damning to herself it could be even more damning to Jeremy than what she said.
For instance, suppose instead of just telling her that his plan included receiving a call that he told her he was going to lie and pretend he received a call from WHF and that in order to try to get police to believe he actually received such call he was going to call her and she tell police he called and told her he was upset after receiving such fictional call. This is even more damning because it makes it even more clear that the call was fictional. Her claim he told her his plan included receiving a call from WHF is still bad but not as direct about the purpose one has to think about it.
If this had been the case it means that when Julie told police about his telling her he received the call that she was helping him lie. She was part of a conspiracy to obstruct justice. If this were true she would have reason to leave out entirely that he had planned to say he received a call form WHF. he fact she mentioned it suggests she truly didn't appreciate he was telling her that he was going to make the call up.