My goodness, what a heart-wrenching story. Thank you so much for sharing this. You are a brilliant storyteller; I felt every bit of this.
Perhaps it helped that I, too, am an adoptee, although I did not end up in a happy adopted environment. It was traumatic and abusive...although not nearly as bad as some endure so I'm grateful for that.
I found my birth mother after 11 years of searching. I was 29. Had a great relationship for a couple of years but...let's just say she has a lot of issues (the rest of the family agrees). I haven't talked to her in many years but I know through family that she has numerous significant health challenges, such as major heart problems and she still smokes and refuses to take care of herself.
Without going into more detail, I will just say this: If it were me with my birth mother, there's not a chance in hell I'd do it. She doesn't value her life or her health, so that's enough reason right there.
But she also doesn't value ME or what it would cost me, either.
You didn't owe your birth mother anything. You didn't ask to be born.
And you're raising your grandson. Heaven forbid but what would happen if your one good kidney ended up with a problem somewhere down the road??
It's one thing to be an organ donor after you no longer need any of them! It's a whole other thing to put your own life and health at risk unless it's someone you really, massively want to help - like your own child or grandchild or a beloved sibling.
I know that no matter what anyone says, you'll likely always wonder and question yourself but I do hope you can let it go. The Universe answered for you; she wasn't meant to have it and the matter was taken out of your hands.
Sending you biiiig hugs. Thank you so much for sharing this story.