Julie couldn't exactly turn down a police car picking her up - Bamber's fault.
After that Bamber could have asked to be left alone while he grieved. However he partied & invited Julie along - Bamber's fault.
Julie in a state of disbelief went along with Bamber. For 20 days.
I don't blame her for going over there at first, but after that, when he allegedly told her that he was responsible, it was entirely her fault that she carried on partying with him. It's not Jeremy's fault that she accepted any of his invitations to party, to go for meals, to go away for weekends - that was down to her.