You made a brilliant point there. Queen Mary made the Queen Mother look like a powder puff by comparison. I would bet the house that Queen Mary was very vocal within the family. I am always astounded when people write about this era and it's controversy, they manage to overlook such an incredibly strong presence as Queen Mary. This, the women reputed to have said,
“You are a member of the British Royal Family: We are never tired and we all love hospitals.”
Or, just plain 'We live to serve and her son David did nothing that he didn't want to do.
So I imagine David's behavior shamed her. From his wild youth to the abdication and his dishonesty and greed, the relationship deteriorated and finally ended, the following excerpt from Wikipedia tells us not only did Q Mary and K George meet Wallis in 1935 but they refused to receive her ever again. It also says:
To me it seems quite obvious that his Mother refused to receive Wallis and Elizabeth followed her lead. It also seems obvious that his brother was definitely not alienated from him because of Elizabeth. Bertie cut him off for pretty obvious reasons, not least because his loving big brother had right royally s****** him over financially.QUOTE]
Could the BRF/government of the day have actually stopped Edward and Wallace returning to the UK? They were still British citizens.