@naomi
Okay. I added "is wealthy" and "is clever" from your 09:04 Tue post and got 5.
It partially answered my next question which was going to be about the timing of the change of behaviour pattern. If I have the sequence right, it was
1. Normal, engaged, kids/grandkids visiting regularly (or she visits them)
2. Starts using Facebook.
3. Makes Friends with remote person who is not part of her real-world life.
4. Becomes more withdrawn
5. Drinking more
6. Unfriended by remote person
7. Yet more withdrawn
8. Husband retires
Now, if the husband being home all the time, which is a large change in the household dynamic, caused little or no perceptible change in her degenerated behaviour, then the unfriending looks more like the final straw but that doesn't make it the trigger point for the start of the slide.
A long-winded way of saying that your instincts were probably correct and, barring new discoveries about goings on coincident with starting on Facebook, then it's the Facebook activity which started the slide.
I've heard opinions expressed that Facebook is a glorified one-upmanship contest "look at me and how fabulous my life is and my adorable family". This may have been how I landed on that page about "narcissistic supply". If one can get peer approval, without rising from the sofa, why go to all the effort of stepping out the front door, where you can only extract approval from a tiny subset of your reams of FB 'frenz'?
Zuckerberg's original design was to serve yuppie fraternity pals, so they could compare girlfriends, shout the odds, brag about their burgeoning careers and so on. If your life just doesn't measure up to the shiny, happy, people, you are going to end up down in the dumps.
That's obviously not applicable to a well off person, like her but I'm trying to say that constantly comparing one's life and achievements to others who are having a better time of it than you is corrosive to the 'soul'.
Note, I am just exploring ideas. They will likely be wrong but it's a process of elimination. The professional therapist has been tried and their opinions dismissed; what chance do we amateurs have?
I'm curious whether NHS counselling has progressed beyond the 1 hour per 6 months that I was offered (~15 years ago) I wanted them to 'fix' me so I could go back to work, before my sick pay ran out but I was low priority, compared to the local addicts, bridge jumpers and other, fully wrecked individuals. We now have increasing victims of domestic and sexual abuse, trafficking, PTSD, war refugees so how anyone else gets a look in, I cannot imagine. We need more trained counsellors, full stop.
If you could spare the time, would it be constructive to visit and just observe her routine for an hour? Would she just blank you and do stuff on the computer or would she put it away until after you leave?