It also begs the question why she wasn't considered an accessory?
Jeremy would have to have admitted they did talk about it to implicate her.
She claimed she thought he was just blowing off steam and not seriously going to do it.
Unless she actually did something to help him, even if only encouraging him to do it, she can't be considered a co-conspirator.
At best they could get her for obstruction of justice for lying but sheframed her new statement as supplemental not that she previously lied. She said she didn' tell information she knew that ocudl have helped she didn't lie. If Jeremy came out and said she's full of crap at 3AM I told her the family had been killed then in that case she lied in all her statements to conceal her full knowledge.
There is no obligation to tell every detail but you can't lie and not mentioning that would be an outright lie. Only Jeremy could reveal though the true extent of her knowledge and participation. For all we know she encouraged him. Of course she is going to say it disgusted her, she's not going to admi tshe thought killing them would result in them mattying and living a weathy good life so she welcomed his plan.
That leaves only Jeremy to implicate her since she didn't implicate herself.
When people who made ommissions come clean they are not prosecuted even if they did lie originally because they ended up coming clean. The exception to this rule is if the newest statements still contained falsehoods to obstruct justice by concealing what truly happened. You have the right to remain silent and not implicate yourself but you can't tell half the truth and lie about the rest to protect yourself or someone else that is still obstruction. So either you shut up entirely or you have to be honest.
Short of Jeremy saying her most recent story was only partially true and that she played a bigger role than she claims who else could testify to such? MAYBE Collins if he had also been privy to th emurders and was also part of the conspiracy. But he would have to implicate himself and Jeremy to implicate Julie.
So at the end of the day the only people who could establish Julie was an accomplice in some form would have to harm themselves in order to expose whatever role she might have played.