Lookout, hello
Rightly or wrongly, I get the impression that Julie probably wasn't on close terms with any of Jeremy's family and as Jeremy seemed not to be closely connected either, therefore not spending time with them, I think it reasonable to assume that Julie didn't either. There would be no reason to think that she would have spent time or socialzed with Sheila apart from Jeremy. I think you may be correct in your assessment of Julie as spiteful.
Hi April,,,JM would certainly have picked up on Sheilas' illness,which would have given her another string to her bow in that because Jeremy wasn't as quick-thinking as she was,,that whatever was fed to Jeremy,it would sound convincing..Such as the fact that when charged,,it was said that Jeremy said that his sister was a " nutter ".Not his language,,but that which was fed to him. He was so brainwashed by JM,that he was beginning to speak her language and think her thoughts.
Her psyche would have been working overtime.