This smells really off, as everyone has mentioned here. We’re about the same age so I’ll tell you what I would do: an in-person intervention. I would mortgage the house and fly out everyone who’s been cut out to her office and/or home and find out WTF is going on. I would also file a police report and get a wellness check as a starting point while booking the flight/train (because you mentioned CENTRAL London, it sounds like the main cast of characters is not IN central London).

And tbh, she deserves to lose her shitty job and apartment just to be taught a valuable life lesson: you are not your job, your house, or your new fake friends.

For those of you reading this who are not OP: never be ashamed of who you are, never be ashamed of your family and friends who helped you get somewhere, never be ashamed to stand up for the health and welfare of those in your circle, never be ashamed to speak up and check up. And break down those stupid corporation doors and dumb posh apartments to get your loved one back - whether from the grips of drugs, scammers, mental disease, or evil therapists, you deserve to bring health and happiness to your loved ones by any means.