Glad you were able to see the records Morgantoo.
I don't know what cerebral softening means, as my 2 x g.aunt (she married my g.grandmother's brother and she was the sister of my g.grandfather!), died, at home, of softening of the brain of 2 months in 1881 when she was only 21. She had had a baby in January 1881, who died of bronchitis in March 1881, then my g.g.aunt died in June 1881. I doubt she had dementia at 21 and I don't know of anyone dying of depression/melancholia (unless it was suicide and there is nothing like that on the death cert).
There are various explanations on the internet, it seems to have been a "cover all" in the 19th century, before doctors knew what was really happening. So your g.g.grandmother could have had a stroke or dementia, and my g.g.aunt could have had encephalitis or other infection (my daughter in law had encephalitis after the birth of her first child in 1990 and she ended up in intensive care. She was treated with intravenous aciclovar which had recently become available and, fortunately, made a good recovery.
Lizzie