Your daughter is around the same age as mine, with what sounds like similar nature and interests, and similar experience of life as it is now for kids their age.
I too became an only child in similar circumstances as your daughter, losing a little sister who was aged seven, to cancer, when I was ten, leaving me as an only child, so I resonate with your story there too. I am very sorry to hear of your loss.
My mother, passed away now, bless her soul, did her best to manage, but I am sure she never felt it was enough, in a cruel world.
You absolutely can’t, and mustn’t blame yourself for losing a child to cancer.
If of any help, I think you are a brilliant Mum, and I am sure your daughter will be just fine, thanks to your conditioning.
Keep up the good work, you are doing great. Thanks for posting, and keep writing!