I shouldn't have read this. I knew it would make me bawl, and it did. My dad went into a nursing home last fall after three years in assisted living. He has been in hospice care in that nursing home since January.
It is the worst torture I could ever imagine. I related to every single thing you said here. I broke down when you described walking into the room each time, wondering what fresh hell awaited. God, that is exactly what it feels like. Most visits are realizing how much worse things are. Every now and then, my dad says, "Hey, it's my daughter."
The only comfort I have is that I now have proof that he knows I'm there even when it seems he doesn't. On the few lucid days I see him, he'll describe to me what I said to him and what day I came last - even though at the time, he was staring at the ceiling and couldn't speak. He KNOWS.
Your grandma knows - and in a good way. She knows you love her. She knows you are coming to be with her. I'm pretty sure that's true.
And no, it's not monstrous to wish you could help her leave this life. I wish that every day for my dad.
Hugs. <3