Your mum is where she is at due to a long string of decisions she has made over the years. This situation with nursing homes suddenly comes upon older folk. Then they find out how very vulnerable they were. But by then if they have slammed the door in the face of those who cared over so many years, the caring person is not in much of a position to help.
Be kind to her in whatever way you can. Be supportive but know your limitations. Don't take on a fight that was probably lost years ago. However, with kindness and genuine love it is possible to win something. Maybe right at the end she finds out she was wrong about WTBS and apologises to you.
Millions now living will never die - I know several who have died very upset having wasted their lives. But it only kicks in at the end when all hope is gone.
Kindness, comfort and consolation - that's what I'd aim at. And take her some treats. But I appreciate I don't know your situation, so you know what's appropriate for your situation.