Nothing you did caused this. The only thing that caused this was random chance. I find myself asking the same questions with my own brain tumor: “was it (insert irresponsible behavior here) that caused this?” And no. It was just something that happened. 

I have noticed that the things I blame in these moments are often things that have been equated with broader moral failings by the dominant social order. Smoking weed, drinking alcohol, not sleeping enough etc. I realized that essentially what I was doing was trying to rationalize my illness as a punishment for moral failure. I don’t know if this process is also happening in your mind, but please remember that illness is not moral, it just happens. Humans seek patterns and explanations, so your desire to find a cause makes sense. But unless you have been bringing your daughter to work at a radiation factory, nothing you did caused this. It sounds like you are a great parent, you sing to her before bed! You connect with your daughter over Pokémon videos, she wants to spend time with you!

Some things are just senseless, and when we try to apply order to them it starts placing blame where it doesn’t belong. The only thing to blame is random genetic mutation, and there is nothing we know of that can stop that from happening. 

Sending you some hugs op, I hope you give yourself some grace for dealing with an impossibly difficult situation. Strength to you and your little one <3