I don't think you can apply generalisations to June's circumstances as everyone is different in the way they cope with situations. Whatever the reasons, there was no justification for what Jeremy did.
If by "June's circumstances" you mean the severe depression she suffered as a result of adopting SC resulting in in-patient psychiatric care and electro-convulsive treatment, I think we need to also consider how SC coped with June's severe depression and the loss of yet another 'primary caregiver'. I should point out here that I do not blame June in any shape or form; the blame must lie with the authorities that approved June as a suitable adopter and Dr Ferguson for not alerting social services and allowing SC to remain in the care of NB and June. The fact they were allowed to go on and adopt another child beggars belief.
Imo anyone interested in the WHF case needs to understand 'Attachment'. It is not some airey-fairy concept. It is one of the most widely researched aspects of psychology. I've just Googled the following and noted the number of hits:
Attachment and adoption = 62,000,000
Attachment and violence = 46,300,000
Attachment and suicide = 11,200,000
Attachment and neuroscience = 1,380,000
Attachment and maternal depression 206,000
Attachment affects all of us from the cradle to the grave
https://www.youtube.com/watch?v=6D-9ylhnA7khttps://www.youtube.com/watch?v=VAAmSqv2GV8