Colin in his book stated that Sheila expressed her thoughts by writing and drawing as she hadn't been blessed like most who would have expressed verbally with a good rant now and again to get it off their chests.
The diaries in this case would have been vital but obviously EP didn't want/wish to promote them in any way and neither did the relatives who I believe had taken charge of them,being " private and personal "!!
But surely, Lookout, they were Colin's memories of when they were together. They hadn't been together for years. From what you've told us, countless times, Sheila had been BRILLIANT at expressing herself verbally -I guess she felt she had to resort to throwing things because she didn't feel heard- it seems to me that it may have been Colin who shied away from confrontation.
I have no idea where the diaries were located -I don't imagine she took them everywhere but I'll allow for the possibility of a lockable 5 year diary- but if the police found them/it at WHF, HAD they contained suicidal thoughts, they'd have been a perfect counter-balance to the family's claims. If Jeremy had found them, for certain sure, he'd have handed them to the police. If they said what you're hoping, he very probably wouldn't be in prison now. However, if the relatives -according to you, nasty conniving people determined to do Jeremy out of his birthright- had found it/them, do you REALLY believe they'd have handed the police ANYTHING which suggested that Sheila MAY have committed such a crime, ESPECIALLY after allegedly going to all that trouble to frame Jeremy?