Dear Donna,
I also am a himmylover; raised a few litters of the darlings!
We also have in common that my mother succumbed to dementia and had to finally be kept in a safe place. I think that you should say what you are comfortable with saying, and that mom likely will not remember any of it. But you will, and you can patiently repeat it as long as you feel the need.
This is nothing whatsoever about you except that you have to mourn the loss. You kept good care of your mom and now still are doing what is necessary for her safety and health, and even her dignity. And, you have to mourn this loss which can seem worse than if she died, because she very well may exhibit normal dementia symptoms over what is impossible for her to understand.
We kept mom in my home, then with a caretaker then finally in a locked facility after she no longer knew what she was doing and that was not safe. We (me and my siblings) learned the hard way to do the hard things, after mom escaped and got lost a couple of times. She was found wandering the streets. We had to make her clothes zip where she could not reach just to keep her diapered and dressed. She just lost ability to understand reason, and she just wanted to explore and wander. Of course we were responsible to make sure she was fed, clean and safe.
That is ALL you are doing...what any loving daughter would do. Where she is at in her life is not your fault. Giving her up to be cared for in a safe place is the most loving thing you can do for her. Seriously, I doubt whether telling her anything would help her adjust. My mom did make this health directive when she had her mental capacities. But whether or not your mother wanted these things, this is the way it is now. All you can do is what is best, and be calm around her, then when alone bawl your eyes out because she is lost to you, and it's worse than death in our minds because she is still alive but we can't reach her. My heart breaks for myself that I went through similar grief and confusion, and I still miss my mom, though she forgot finally who I am, how to swallow and how to breathe and she passed away years ago.
My heart breaks for you. But I also know you are strong enough to do what is right for mom and you can do your grief work when grief comes up, and get through this.
I will be praying for you. Life can be so brutal.
God is blessing you.
Much love,