I don't know the woman, or the interaction she had with Jeremy, so I don't really feel I could say I knew what she was thinking at that time, or indeed at any time.
I can however see a number of possibilities. My current thoughts are that she simply didn't believe JB could have done it and was probably doing her boyfriend a favour by identifying the bodies so that he wouldn't have to.
Where there's a murder case,the belief in imagining that the person you're " in love with had nothing to do with it ", has to be so strong as to render it an impossibility that that person had anything to do with it at all.
Had Julie genuinely loved him ? Because judging by her actions in court,she didn't. You don't tear into someone like she did without feeling any pangs of sorrow,or was that why she cried uncontrollably when being questioned by Rivlin ? Did she,or didn't she want to be there at that point,or was she happier letting off steam for the prosecution side ? If that was the case she didn't have any love for him.
I can't really fathom the woman out apart from the fact she was mixed up.
It wasn't a case that she " did Jeremy a favour ". He simply couldn't face it,like a lot of people can't,so don't knock him for that. According to CAL,she went on behalf of Jeremy as she was nearer to family than anyone else. Colin hadn't wanted to go,that's why he'd asked Heather,until SJ put a stop to that arrangement.