It is hard.
My family went through that for over ten years with my mom and it was Covid that took her on the very last day of 2020. There is a bit of a tale similar to yours in each of my and my siblings' experience with it.
As it was, one of my younger two siblings was assigned executor of her estate and the other was a major player in mom's daily life. Mom lived with her partner until the last year, the separation hastened her decline along with Covid restrictions and her not understanding why she was alone in a facility and couldn't go anywhere, nobody could visit. My siblings did everything they could for her, I was their counsel. The executor was always driven by a premonition of mom passing alone in a facility that was a haunting issue in the last couple years and it was very psychologically and emotionally taxing for both siblings. Yet through the last days we knew she would die from Covid and we were terrified about it too, but we all had wished she would pass easily in her sleep to end her suffering. It is not a crime or a sin to wish someone stop suffering. We shared many discussions about it.
Death is part of life, none of us escape it. It is in the way we live our lives with passion and conviction that matters in the end. What we left with those who survive us... the real substance of life, it's only the physical that actually leaves us. You can let her body go, she's done with it and, yes, it is a merciful desire to wish her peace after all.
This is the hard part but you'll get through it. Be comforted in knowing you did what you could for her and that, respecting her life, is all you can do for her. We had this discussion a few years ago, you are doing the right things, you can take comfort in knowing that you did give a shit and took the issue by the horns and lead it to its natural conclusion. It's more of a physical thing if she's not lucid anymore.
You have done well, Grasshopper, take the positive energy from knowing this and apply it to the next thing that needs your attention as you move forward. The goal should be to take better care of yourself for now, you deserve it.
Edit history
= new reply since forum marked as read