Absolutely. However, it is possible that she simply didn't believe it possible that Jeremy had carried out what she had put down to immature fantasy.
Her own version of events is that the reality set in over the next few weeks and then went to the police.
Of course, she might just be a bit 'sick'. 
I imagine her version is probably the truth, it does make sense when you think about it that the idea may have built in her head, especially if she was at times surrounded by people who suspected his guilt, was aware of the way JB was behaving etc.
Rightly or wrongly her belief in his guilt could have become a driving force which she had to express. To my mind it doesn't prove JB's guilt but it does make it easier to understand JM's actions at the time.
Whether she was right or wrong in her belief of JB's guilt she was a gift to EP.